#include "bits/stdc++.h"
using namespace std;
#ifdef Nero
#include "Deb.h"
#else
#define deb(...)
#endif
const int md = (int) 1e9 + 7;
const int N = 503;
int iv[N];
int len[N * 2];
int dp[N][N * 2];
long long a[N], b[N];
void add(int& x, int y) {
x += y;
if (x >= md) x -= md;
}
int mul(int x, int y) {
return (int) ((long long) x * y % md);
}
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int n;
cin >> n;
vector<long long> c;
for (int i = 1; i <= n; ++i) {
cin >> a[i] >> b[i];
c.push_back(a[i]);
c.push_back(++b[i]);
}
sort(c.begin(), c.end());
c.resize(unique(c.begin(), c.end()) - c.begin());
for (int i = 1; i <= n; ++i) {
a[i] = upper_bound(c.begin(), c.end(), a[i]) - c.begin();
b[i] = upper_bound(c.begin(), c.end(), b[i]) - c.begin();
}
iv[1] = 1;
for (int i = 2; i <= n; ++i) {
iv[i] = mul(md - md / i, iv[md % i]);
}
int m = (int) c.size();
for (int i = 1; i < m; ++i) {
len[i] = c[i] - c[i - 1];
}
for (int i = 0; i <= m; ++i) {
dp[0][i] = 1;
}
for (int i = 1; i <= n; ++i) {
for (int j = a[i]; j < b[i]; ++j) {
int prod = len[j], cnt = 1;
for (int k = i - 1; k >= 0; --k) {
add(dp[i][j], mul(dp[k][j - 1], prod));
if (a[k] <= j && j < b[k]) {
prod = mul(prod, iv[cnt + 1]);
prod = mul(prod, len[j] + cnt);
cnt++;
}
}
}
for (int j = 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 << '\n';
return 0;
}
