#include <bits/stdc++.h>
using namespace std;
#define int long long
const int maxn = 1e3 + 5, mod = 1e9 + 7;
int dp[maxn][maxn], pre[maxn][maxn],sum_dp[maxn],val[2*maxn],L[maxn],R[maxn],inv[maxn];
int binpow(int a, int b){
int res = 1;
while(b){
if(b & 1) res =res * a % mod;
a = a * a % mod;
b /= 2;
}
return res;
}
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
// freopen("BOAT.inp", "r", stdin);
// freopen("BOAT.out", "w", stdout);
int n; cin >> n;
int cnt = 0;
for(int i = 1; i <= n; i++){
cin >> L[i] >> R[i];
val[++cnt] = L[i];
val[++cnt] = R[i] + 1;
}
sort(val + 1, val + cnt + 1);
cnt = unique(val + 1, val + cnt + 1) - (val + 1);
for(int i = 1; i <= n; i++) inv[i] = binpow(i, mod - 2);
for(int i = 0; i <= cnt; i++) sum_dp[i] = 1;
for(int i = 1; i <= n; i++){
int idl = lower_bound(val + 1, val + cnt + 1, L[i]) - val;
int idr = lower_bound(val + 1, val + cnt + 1, R[i] + 1) - val;
for(int j = idl; j < idr; j++)
for(int k = 1; k <= i; k++) pre[j][k] = dp[j][k];
for(int j = idl; j < idr; j++){
int len = (val[j + 1] - val[j]);
dp[j][1] = (dp[j][1] + sum_dp[j-1] * len) % mod; //k = 1
for(int k = 2; k <= i; k++){ //k > 1
dp[j][k] = (dp[j][k] + pre[j][k - 1] * (len - k + 1) % mod * inv[k] % mod) % mod;
}
}
for(int j = 1; j < cnt; j++){
sum_dp[j] = sum_dp[j - 1] + 1;
for(int k = 1; k <= i; k++) sum_dp[j] = (sum_dp[j] + dp[j][k]) % mod;
}
}
int ans = 0;
for(int j = 1; j < cnt; j++){
for(int k = 1; k <= n; k++) ans = (ans + dp[j][k]) % mod;
}
cout << ans;
}
