#include <bits/stdc++.h>
#define nl "\n"
#define no "NO"
#define yes "YES"
#define fi first
#define se second
#define vec vector
#define task "main"
#define _mp make_pair
#define ii pair<int, int>
#define sz(x) (int)x.size()
#define all(x) x.begin(), x.end()
#define evoid(val) return void(std::cout << val)
#define FOR(i, a, b) for(int i = (a); i <= (b); ++i)
#define FOD(i, b, a) for(int i = (b); i >= (a); --i)
#define unq(x) sort(all(x)); x.resize(unique(all(x)) - x.begin())
using namespace std;
template<typename U, typename V> bool maxi(U &a, V b) {
if (a < b) { a = b; return 1; } return 0;
}
template<typename U, typename V> bool mini(U &a, V b) {
if (a > b) { a = b; return 1; } return 0;
}
const int N = (int)500 + 9;
const int mod = (int)1e9 + 7;
void prepare(); void main_code();
int main() {
ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
if (fopen(task".inp", "r")) {
freopen(task".inp", "r", stdin);
freopen(task".out", "w", stdout);
}
const bool MULTITEST = 0; prepare();
int num_test = 1; if (MULTITEST) cin >> num_test;
while (num_test--) { main_code(); }
}
void prepare() {};
int n, a[N], b[N];
void add(int &a, int b) {
a += b;
if (a >= mod) a -= mod;
}
namespace SUB1 {
int dp[N][N];
void sol() {
dp[0][0] = 1;
a[0] = b[0] = 0;
FOR(i, 0, n - 1) FOR(j, 0, i) if (dp[i][j]) {
add(dp[i + 1][j], dp[i][j]);
if (b[i + 1] > b[j])
add(dp[i + 1][i + 1], dp[i][j]);
}
int res = 0;
FOR(i, 1, n) add(res, dp[n][i]);
cout << res;
}
};
namespace SUB2 {
int S[N];
vector<int> dp[N];
void sol() {
int res = 0;
for(int i = 1; i <= n; ++i) {
int os = 1;
int L = b[i] - a[i] + 1;
S[i] = L;
dp[i].resize(L);
for(int j = 1; j < i; ++j) {
if (a[i] > b[j]) {
add(os, dp[j][S[j] - 1]);
} else if (max(a[i], a[j]) <= min(b[i], b[j])) {
if (a[i] >= a[j]) {
for(int x = 0; x < L; ++x) {
if (x + a[i] - a[j] - 1 >= 0)
add(dp[i][x], dp[j][min(x + a[i] - a[j] - 1, S[j] - 1)]);
}
} else {
for(int x = a[j] + 1; x <= b[i]; ++x) {
add(dp[i][x - a[i]], dp[j][min(x - a[j] - 1, S[j] - 1)]);
}
}
}
}
for(int x = 0; x < L; ++x) {
add(dp[i][x], os);
if (x > 0) add(dp[i][x], dp[i][x - 1]);
}
add(res, dp[i][L - 1]);
}
cout << res;
}
};
int Pow(int a, long long b) {
int res = 1;
for(; b > 0; b >>= 1, a = 1ll * a * a % mod)
if (b & 1) res = 1ll * res * a % mod;
return res;
}
namespace SUB3 {
const int N = 507;
int dp[N][3 * N], f[3 * N][N];
int C[3 * N][N], P[N], inv[N], F[N];
int mul(int a, int b) { return 1LL * a * b % mod; }
int comb(int k, int n) {
return mul(P[n], mul(F[k], F[n - k]));
}
void build(vector<int> val) {
P[0] = 1;
FOR(i, 1, n) P[i] = mul(P[i - 1], i);
F[n] = Pow(P[n], mod - 2);
FOD(i, n - 1, 0) F[i] = mul(F[i + 1], i + 1);
FOR(i, 1, n) inv[i] = Pow(i, mod - 2);
for(int i = 0; i < sz(val); ++i) {
int k = val[i];
// tinh c(x, k) voi x <= min(n, k)
C[i][1] = k;
for(int j = 2; j <= min(n, k); ++j) {
C[i][j] = mul(C[i][j - 1], mul(inv[j], k - j + 1));
}
for(int d = 1; d <= n; ++d) {
// co d option -> dien vao val
for(int z = 1; z <= min(d, k); ++z) {
add(f[i][d], mul(comb(z - 1, d - 1), C[i][z]));
}
}
}
}
const bool DBG = 0;
void sol() {
vector<int> mark;
mark.push_back(0);
for(int i = 1; i <= n; ++i) {
mark.push_back(a[i]);
mark.push_back(b[i]);
mark.push_back(a[i] - 1);
}
unq(mark);
if (DBG) {
cout << "mark: "; for(int x : mark) cout << x << ' '; cout << nl;
}
// can tinh cac doan 1-> va mark[j]-mark[j-1]
vector<int> val;
val.push_back(1);
for(int i = 1; i < sz(mark); ++i)
val.push_back(mark[i] - mark[i - 1]);
unq(val);
build(val);
if (DBG) {
cout << "val: "; for(int x : val) cout << x << ' '; cout << nl;
cout << nl;
}
int m = sz(mark) - 1;
FOR(j, 0, m) dp[0][j] = 1;
for(int i = 1; i <= n; ++i) {
// dp->prefix sum;
int L = lower_bound(all(mark), a[i]) - mark.begin();
int R = lower_bound(all(mark), b[i]) - mark.begin();
if (DBG) cout << "l,r: " << L << ' ' << R << nl;
for(int j = L; j <= R; ++j) {
// dp(i, j)
int lr = (j == L ? mark[j] : mark[j - 1] + 1);
int rr = mark[j];
int id = lower_bound(all(val), rr - lr + 1) - val.begin();
int depth = 1;
dp[i][j] = 0;
for(int k = i - 1; k >= 0; --k) {
// con cai gia tri f->ta tinh duoc luon gia tri
if (DBG) if (i == 3 and j == 3) {
cerr << k << ' ' << " - depth: " << depth << ' ' << dp[k][j - 1] << ' ' << f[id][depth] << nl;
}
add(dp[i][j], mul(dp[k][j - 1], f[id][depth]));
if (a[k] <= lr and b[k] >= rr)
++depth;
}
if (DBG)cout << dp[i][j] << ' ';
}
if (DBG)cout << nl;
for(int j = L + 1; j <= m; ++j)
add(dp[i][j], dp[i][j - 1]);
}
int ans = 0;
for(int i = 1; i <= n; ++i) {
add(ans, dp[i][m]);
}
cout << ans;
}
};
void main_code() {
cin >> n;
long long sum = 0;
for(int i = 1; i <= n; ++i) cin >> a[i] >> b[i], sum += b[i] - a[i] + 1;
if (n <= 500 and sum == n) {
return SUB1::sol(), void();
}
if (n <= 500 and sum <= (int)1e6 + 7) {
return SUB2::sol(), void();
}
SUB3::sol();
}
/* Let the river flows naturally */
