#include <bits/stdc++.h>
using namespace std;
#define int long long
const int N = 1100;
const int MOD = (int)(1e9+7);
int n, m, a[N], b[N], dp[N][N], vv[N];
vector<int> pos;
void init() {
for (int i = 1; i < N; i++)
vv[i] = (i == 1 ? 1 : MOD - MOD / i * vv[MOD % i] % MOD);
}
int sz(int k) {
return pos[k] - pos[k - 1];
}
int32_t main() {
ios::sync_with_stdio(0); cin.tie(0);
init();
cin >> n;
for (int i = 1; i <= n; i++) {
cin >> a[i] >> b[i];
pos.push_back(a[i]);
pos.push_back(b[i] + 1);
}
sort(begin(pos), end(pos));
pos.erase(unique(begin(pos), end(pos)), end(pos));
m = (int) pos.size() - 1;
for (int i = 1; i <= n; i++) {
int sum = 1;
for (int j = 1; j <= m; j++) {
int old = 0;
for (int k = 1; k <= n; k++)
old += dp[j][k];
if (a[i] <= pos[j - 1] && pos[j] <= b[i] + 1) {
for (int k = n; k >= 1; k--)
if (k == 1)
(dp[j][k] += sum * sz(j)) %= MOD;
else
(dp[j][k] += dp[j][k - 1] * (sz(j) - k + 1) % MOD * vv[k]) %= MOD;
}
(sum += old) %= MOD;
}
}
int ans = 0;
for (int i = 1; i <= m; i++)
for (int j = 1; j <= n; j++)
(ans += dp[i][j]) %= MOD;
cout << ans;
}
