/**
* @title Template
*/
#include <iostream>
#include <algorithm>
#include <utility>
#include <numeric>
#include <vector>
#include <array>
#include <cassert>
template <class T, class U>
bool chmin(T &lhs, const U &rhs) {
if (lhs > rhs) {
lhs = rhs;
return true;
}
return false;
}
template <class T, class U>
bool chmax(T &lhs, const U &rhs) {
if (lhs < rhs) {
lhs = rhs;
return true;
}
return false;
}
/**
* @title Chmin/Chmax
*/
class range {
public:
class iterator {
private:
int64_t M_position;
public:
iterator(int64_t position) noexcept: M_position(position) { }
void operator ++ () noexcept { ++M_position; }
bool operator != (iterator other) const noexcept { return M_position != other.M_position; }
int64_t operator * () const noexcept { return M_position; }
};
class reverse_iterator {
private:
int64_t M_position;
public:
reverse_iterator(int64_t position) noexcept: M_position(position) { }
void operator ++ () noexcept { --M_position; }
bool operator != (reverse_iterator other) const noexcept { return M_position != other.M_position; }
int64_t operator * () const noexcept { return M_position; }
};
private:
const iterator M_first, M_last;
public:
range(int64_t first, int64_t last) noexcept: M_first(first), M_last(std::max(first, last)) { }
iterator begin() const noexcept { return M_first; }
iterator end() const noexcept { return M_last; }
reverse_iterator rbegin() const noexcept { return reverse_iterator(*M_last - 1); }
reverse_iterator rend() const noexcept { return reverse_iterator(*M_first - 1); }
};
/**
* @title Range
*/
#include <type_traits>
#include <iterator>
template <class T>
class rev_impl {
public:
using iterator = decltype(std::declval<T>().rbegin());
private:
const iterator M_begin;
const iterator M_end;
public:
rev_impl(T &&cont) noexcept: M_begin(cont.rbegin()), M_end(cont.rend()) { }
iterator begin() const noexcept { return M_begin; }
iterator end() const noexcept { return M_end; }
};
template <class T>
rev_impl<T> rev(T &&cont) {
return rev_impl<T>(std::forward<T>(cont));
}
/**
* @title Reverser
*/
#include <cstdint>
template <class Modulus>
class modular {
public:
using value_type = uint32_t;
using cover_type = uint64_t;
static constexpr value_type mod() { return Modulus::value(); }
template <class T>
static value_type normalize(T value_) noexcept {
if (value_ < 0) {
value_ = -value_;
value_ %= mod();
if (value_ == 0) return 0;
return mod() - value_;
}
return value_ % mod();
}
private:
value_type value;
public:
modular() noexcept : value(0) { }
template <class T>
explicit modular(T value_) noexcept : value(normalize(value_)) { }
template <class T>
explicit operator T() const noexcept { return static_cast<T>(value); }
value_type get() const noexcept { return value; }
modular operator - () const noexcept { return modular(mod() - value); }
modular operator ~ () const noexcept { return inverse(); }
value_type &extract() noexcept { return value; }
modular inverse() const noexcept { return power(mod() - 2); }
modular power(cover_type exp) const noexcept {
modular res(1), mult(*this);
while (exp > 0) {
if (exp & 1) res *= mult;
mult *= mult;
exp >>= 1;
}
return res;
}
modular operator + (const modular &rhs) const noexcept { return modular(*this) += rhs; }
modular& operator += (const modular &rhs) noexcept {
if ((value += rhs.value) >= mod()) value -= mod();
return *this;
}
modular operator - (const modular &rhs) const noexcept { return modular(*this) -= rhs; }
modular& operator -= (const modular &rhs) noexcept {
if ((value += mod() - rhs.value) >= mod()) value -= mod();
return *this;
}
modular operator * (const modular &rhs) const noexcept { return modular(*this) *= rhs; }
modular& operator *= (const modular &rhs) noexcept {
value = (cover_type) value * rhs.value % mod();
return *this;
}
modular operator / (const modular &rhs) const noexcept { return modular(*this) /= rhs; }
modular& operator /= (const modular &rhs) noexcept { return (*this) *= rhs.inverse(); }
bool zero() const noexcept { return value == 0; }
bool operator == (const modular &rhs) const noexcept { return value == rhs.value; }
bool operator != (const modular &rhs) const noexcept { return value != rhs.value; }
friend std::ostream& operator << (std::ostream &stream, const modular &rhs) { return stream << rhs.value; }
friend modular power(modular val, cover_type exp) noexcept { return val.power(exp); }
friend modular inverse(modular val) noexcept { return val.inverse(); }
};
template <uint32_t Val>
struct modulus_impl { static constexpr uint32_t value() noexcept { return Val; } };
template <uint32_t Val>
using mint32_t = modular<modulus_impl<Val>>;
struct runtime_mod { static uint32_t &value() noexcept { static uint32_t val = 0; return val; } };
using rmint32_t = modular<runtime_mod>;
/**
* @title Modint
*/
#include <cstddef>
size_t bit_ppc(const uint64_t x) {
return __builtin_popcountll(x);
}
size_t bit_ctzr(const uint64_t x) {
return x == 0 ? 64 : __builtin_ctzll(x);
}
size_t bit_ctzl(const uint64_t x) {
return x == 0 ? 64 : __builtin_clzll(x);
}
size_t bit_width(const uint64_t x) {
return 64 - bit_ctzl(x);
}
uint64_t bit_msb(const uint64_t x) {
return x == 0 ? 0 : uint64_t(1) << (bit_width(x) - 1);
}
uint64_t bit_lsb(const uint64_t x) {
return x & (-x);
}
uint64_t bit_cover(const uint64_t x) {
return x == 0 ? 0 : bit_msb(2 * x - 1);
}
uint64_t bit_rev(uint64_t x) {
x = ((x >> 1) & 0x5555555555555555) | ((x & 0x5555555555555555) << 1);
x = ((x >> 2) & 0x3333333333333333) | ((x & 0x3333333333333333) << 2);
x = ((x >> 4) & 0x0F0F0F0F0F0F0F0F) | ((x & 0x0F0F0F0F0F0F0F0F) << 4);
x = ((x >> 8) & 0x00FF00FF00FF00FF) | ((x & 0x00FF00FF00FF00FF) << 8);
x = ((x >> 16) & 0x0000FFFF0000FFFF) | ((x & 0x0000FFFF0000FFFF) << 16);
x = (x >> 32) | (x << 32);
return x;
}
/**
* @title Bit Operations
*/
template <class T>
class fenwick_tree {
public:
using value_type = T;
using size_type = size_t;
private:
std::vector<value_type> M_tree;
public:
fenwick_tree() = default;
explicit fenwick_tree(size_type size) { initialize(size); }
void initialize(size_type size) {
M_tree.assign(size + 1, value_type{});
}
void add(size_type index, const value_type& x) {
++index;
while (index <= size()) {
M_tree[index] += x;
index += bit_lsb(index);
}
}
value_type get(size_type index) const {
++index;
value_type res{};
while (index > 0) {
res += M_tree[index];
index -= bit_lsb(index);
}
return res;
}
value_type fold(size_type l, size_type r) const {
if (l == 0 && r == 0) return value_type{};
if (l == 0) return get(r - 1);
return get(r - 1) - get(l - 1);
}
size_type size() const {
return M_tree.size() - 1;
}
};
/**
* @title Fenwick Tree
*/
using i32 = int32_t;
using i64 = int64_t;
using u32 = uint32_t;
using u64 = uint64_t;
constexpr i32 inf32 = (i32(1) << 30) - 1;
constexpr i64 inf64 = (i64(1) << 62) - 1;
using m32 = mint32_t<1000000007>;
int main() {
size_t N;
std::cin >> N;
std::vector<std::pair<i32, i32>> boat(N);
i64 sum = 0;
for (auto &p: boat) {
std::cin >> p.first >> p.second;
sum += p.second - p.first;
}
assert(sum <= 1000000);
std::vector<i32> vec;
vec.reserve(sum + 1);
vec.push_back(0);
for (auto p: boat) {
for (auto i: range(p.first, p.second + 1)) {
vec.push_back(i);
}
}
std::sort(vec.begin(), vec.end());
vec.erase(std::unique(vec.begin(), vec.end()), vec.end());
fenwick_tree<m32> dp(vec.size());
dp.add(0, m32(1));
for (auto p: boat) {
i32 st = std::lower_bound(vec.begin(), vec.end(), p.first) - vec.begin();
for (auto i: rev(range(st, st + p.second - p.first + 1))) {
dp.add(i, dp.get(i - 1));
}
}
std::cout << dp.get(dp.size() - 1) - m32(1) << '\n';
return 0;
}
