#include <iostream>
#include <iomanip>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <cmath>
#include <cstring>
#include <cassert>
#include <string>
#include <set>
#include <map>
#include <random>
#include <bitset>
#include <string>
#include <unordered_set>
#include <unordered_map>
#include <deque>
#include <queue>
#define rep(i, n) for (int i = 0; i < (n); i++)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
using namespace std;
using ll = long long;
using ul = unsigned long long;
using ld = long double;
const int N = 1001;
const ll MOD = 1e9 + 7, M2 = MOD * MOD;
ll a[N], b[N], ps[N][N], c[N][N], cd[N][N], rev[N], cs[N][N], dp[N][N];
ll pw(ll x, ll k) {
ll r = 1;
while (k) {
if (k & 1)
r = r * x % MOD;
k >>= 1;
x = x * x % MOD;
}
return r;
}
int main() {
ios_base::sync_with_stdio(0); cin.tie(0);
ll n, d;
cin >> n;
vector<ll> li;
rep(i, n) {
cin >> a[i] >> b[i];
b[i]++;
li.push_back(a[i]);
li.push_back(b[i]);
}
sort(all(li));
li.resize(unique(all(li)) - li.begin());
int m = li.size();
rep(i, n) {
a[i] = lower_bound(all(li), a[i]) - li.begin();
b[i] = lower_bound(all(li), b[i]) - li.begin();
rep(j, m)
ps[j][i + 1] = ps[j][i] + (a[i] <= j && j < b[i]);
}
rep(i, n + 1) {
c[i][0] = 1;
for (int j = 1; j <= i; j++)
c[i][j] = (c[i - 1][j - 1] + c[i - 1][j]) % MOD;
rev[i] = pw(i, MOD - 2);
}
rep(i, m - 1) {
d = li[i + 1] - li[i];
cd[i][1] = d;
for (int j = 1; j < n; j++)
cd[i][j + 1] = cd[i][j] * (d - j) % MOD * rev[j + 1] % MOD;
for (int j = 1; j <= n; j++) {
for (int k = 1; k <= j; k++) {
cs[i][j] += c[j - 1][k - 1] * cd[i][k];
if (cs[i][j] >= M2)
cs[i][j] -= M2;
}
cs[i][j] %= MOD;
}
}
rep(i, n) {
for (int j = a[i]; j < b[i]; j++) {
dp[i + 1][j] = cs[j][ps[j][i + 1]];
if (j)
rep(k, i + 1) {
dp[i + 1][j] += dp[k][j - 1] * cs[j][ps[j][i + 1] - ps[j][k]];
if (dp[i + 1][j] >= M2)
dp[i + 1][j] -= M2;
}
dp[i + 1][j] %= MOD;
}
rep(j, m)
dp[i + 1][j + 1] = (dp[i + 1][j] + dp[i + 1][j + 1]) % MOD;
}
ll ans = 0;
rep(i, n + 1) {
ans = (ans + dp[i][m]) % MOD;
}
cout << ans;
}
