//qoj2
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

const ll P = 1e9 + 7;
const int N = 510, M = 1010;
int n, a[N], b[N], pl[M];
ll f[N][M], g[N][M], h[N][M];
ll fac[N], inv[N];

ll qp(ll x, ll y){
	ll ans = 1;
	while(y){
		if(y & 1){
			ans = ans * x % P;
		}
		x = x * x % P;
		y >>= 1;
	}
	return ans;
}

int main(){
	scanf("%d", &n);
	fac[0] = 1;
	for(int i = 1; i <= n; ++ i){
		fac[i] = fac[i-1] * i % P;
		scanf("%d%d", &a[i], &b[i]);
		pl[i] = a[i];
		pl[i+n] = b[i] + 1;
	}
	inv[n] = qp(fac[n], P-2);
	for(int i = n-1; i >= 0; -- i){
		inv[i] = inv[i+1] * (i+1) % P;
	}
	sort(pl + 1, pl + n + n + 1);
	int m = unique(pl + 1, pl + n + n + 1) - pl - 1;
	for(int i = 1; i <= n; ++ i){
		a[i] = lower_bound(pl + 1, pl + m + 1, a[i]) - pl;
		b[i] = lower_bound(pl + 1, pl + m + 1, b[i] + 1) - pl - 1;
	}
	f[0][0] = 1;
	for(int j = 0; j < m; ++ j){
		g[0][j] = 1;
	}
	for(int j = 1; j < m; ++ j){
		h[0][j] = 1;
		ll val = 1;
		for(int i = 1; i <= n; ++ i){
			val = val * (pl[j+1] - pl[j] + i - 1) % P;
			h[i][j] = val * inv[i] % P;
		}
	}
	for(int i = 1; i <= n; ++ i){
		// printf("%d %d\n", a[i], b[i]);
		for(int j = 1; j < m; ++ j){
			if(j < a[i] || j > b[i]){
				continue;
			}
			int cnt = 0;
			for(int k = i; k >= 1; -- k){
				if(a[k] <= j && j <= b[k]){
					++ cnt;
				}
				f[i][j] = (f[i][j] + g[k-1][j-1] * h[cnt][j]) % P;
			}
		}
		for(int j = 1; j <= m; ++ j){
			g[i][j] = (g[i][j-1] + f[i][j]) % P;
		}
	}
	ll ans = 0;
	for(int i = 1; i <= n; ++ i){
		for(int j = 1; j < m; ++ j){
			ans = (ans + f[i][j]) % P;
		}
	}
	printf("%lld\n", ans);
	return 0;
}