#include <bits/stdc++.h>
using namespace std;
const int Mod = 1e9 + 7;
void add(int &x, const int &y){
x += y;
if ( x >= Mod ) x -= Mod;
}
int inv[501];
int binPow(int x, int y){
int res = 1;
for (; y > 0; x = x * 1LL * x % Mod, y >>= 1 ){
if ( y & 1 ) res = res * 1LL * x % Mod;
}
return res;
}
signed main(){
for ( int i = 0; i <= 500; i++ ) inv[i] = binPow(i, Mod - 2);
int n; cin >> n;
vector <int> a(n), b(n), p;
for ( int i = 0; i < n; i++ ){
cin >> a[i] >> b[i];
p.push_back(a[i]);
p.push_back(b[i]);
}
sort(begin(p), end(p));
p.resize(unique(begin(p), end(p)) - begin(p));
int m = size(p);
vector <vector<int>> dp(m, vector <int> (n + 1));
dp[0][0] = 1;
for ( int i = 0; i + 1 < m; i++ ){
int len = p[i + 1] - p[i];
for ( int j = 0; j <= n; j++ ){
add(dp[i + 1][j], dp[i][j]);
if ( j + 1 <= n ){
add(dp[i][j + 1], dp[i][j]);
if ( a[i] <= p[i] && p[i + 1] <= b[i] + 1 ){
int sum = 0, id = 0, binom = 1;
for ( int k = j; k < n; k++ ){
if ( a[k] <= p[i] && p[i + 1] <= b[k] + 1 ){
id += 1;
if ( id <= len ){
binom = binom * 1LL * (len - id + 1) % Mod * inv[id] % Mod;
add(sum, binom);
}
add(dp[i + 1][k + 1], dp[i][j] * 1LL * sum % Mod);
}
}
}
}
}
}
cout << (dp[m - 1][n] - 1 + Mod) % Mod << '\n';
}
