#include <cmath>
#include <functional>
#include <fstream>
#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <set>
#include <map>
#include <list>
#include <time.h>
#include <math.h>
#include <random>
#include <deque>
#include <queue>
#include <unordered_map>
#include <unordered_set>
#include <iomanip>
#include <cassert>
#include <bitset>
#include <sstream>
#include <chrono>
#include <cstring>
#include <numeric>
using namespace std;
typedef long long ll;
const int M = (int)1e9 + 7;
const int FACTN = 300000 + 7;
int add(int a, int b) {
a += b;
if (a >= M) return a - M;
if (a < 0) return a + M;
return a;
}
int mul(int a, int b) {
return a * (ll)b % M;
}
int add(int a, int b, int c) {
return add(add(a, b), c);
}
int mul(int a, int b, int c) {
return mul(mul(a, b), c);
}
int add(int a, int b, int c, int d) {
return add(add(a, b, c), d);
}
int mul(int a, int b, int c, int d) {
return mul(mul(a, b, c), d);
}
int add(int a, int b, int c, int d, int e) {
return add(add(a, b, c, d), e);
}
int mul(int a, int b, int c, int d, int e) {
return mul(mul(a, b, c, d), e);
}
int add(int a, int b, int c, int d, int e, int f) {
return add(add(a, b, c, d, e), f);
}
int mul(int a, int b, int c, int d, int e, int f) {
return mul(mul(a, b, c, d, e), f);
}
int add(int a, int b, int c, int d, int e, int f, int g) {
return add(add(a, b, c, d, e, f), g);
}
int mul(int a, int b, int c, int d, int e, int f, int g) {
return mul(mul(a, b, c, d, e, f), g);
}
int add(int a, int b, int c, int d, int e, int f, int g, int h) {
return add(add(a, b, c, d, e, f, g), h);
}
int mul(int a, int b, int c, int d, int e, int f, int g, int h) {
return mul(mul(a, b, c, d, e, f, g), h);
}
int pw(int a, int b) {
int r = 1;
while (b) {
if (b & 1) r = mul(r, a);
a = mul(a, a);
b /= 2;
}
return r;
}
int dv(int a, int b) {
return mul(a, pw(b, M - 2));
}
void addup(int& a, int b) {
a = add(a, b);
}
void mulup(int& a, int b) {
a = mul(a, b);
}
void dvup(int& a, int b) {
a = dv(a, b);
}
int fact[FACTN], ifact[FACTN];
void computeFACT() {
fact[0] = 1;
for (int i = 1; i < FACTN; i++) fact[i] = mul(fact[i - 1], i);
ifact[FACTN - 1] = dv(1, fact[FACTN - 1]);
for (int i = FACTN - 2; i >= 0; i--) ifact[i] = mul(ifact[i + 1], i + 1);
}
int getCOMB(int n, int k) {
return mul(fact[n], mul(ifact[k], ifact[n - k]));
}
int dumb(vector<pair<int, int>> segs)
{
int n = (int)segs.size();
vector<vector<int>> dp(n);
for (int i = 0; i < n; i++)
{
assert(segs[i].first <= segs[i].second);
dp[i].resize(segs[i].second - segs[i].first + 1, 1);
}
for (int i = 0; i < n; i++)
{
for (int j = 0; j < i; j++)
{
for (int y = segs[i].first; y <= segs[i].second; y++)
{
if (segs[j].second <= y - 1)
{
addup(dp[i][y - segs[i].first], dp[j].back());
}
else
{
if (segs[j].first <= y - 1)
{
addup(dp[i][y - segs[i].first], dp[j][y - 1 - segs[j].first]);
}
}
}
}
int cur = 0;
for (auto& it : dp[i])
{
addup(cur, it);
it = cur;
}
}
int sol = 0;
for (int i = 0; i < n; i++)
{
addup(sol, dp[i].back());
}
return sol;
}
signed main()
{
#ifdef ONPC
FILE* stream;
freopen_s(&stream, "input.txt", "r", stdin);
#else
ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#endif
int n;
cin >> n;
vector<pair<int, int>> v(n);
for (auto& it : v)
{
cin >> it.first >> it.second;
}
cout << dumb(v) << "\n";
return 0;
}
