#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int MAXN = 501;
const ll MOD = 1e9 + 7;
ll dp[MAXN][MAXN],dp2[MAXN][2*MAXN],somatorio1[MAXN],somatorio2[MAXN];
ll precalc[MAXN],A[MAXN],B[MAXN],N,M;
vector<ll> intervalos;
ll binary_expo(ll val,ll pot){
if(pot == 0) return 1LL;
if(pot % 2 == 0){
ll davez = binary_expo(val,pot/2);
return (davez*davez) % MOD;
}
return (val*binary_expo(val,pot-1)) % MOD;
}
int main(){
cin >> N;
for(int i = 1;i<=N;i++){
cin >> A[i] >> B[i];
B[i]++;
intervalos.push_back(A[i]);
intervalos.push_back(B[i]);
}
sort(intervalos.begin(),intervalos.end());
intervalos.erase(unique(intervalos.begin(),intervalos.end()),intervalos.end());
M = intervalos.size() - 2;
ll tot = 0;
for(int v = M;v>=0;v--){
memset(dp,0,sizeof(dp));
memset(somatorio2,0,sizeof(somatorio2));
ll tam = intervalos[v+1] - intervalos[v];
ll vaiate = min(tam,N);
for(ll i = 2;i<=vaiate;i++){
precalc[i] = (tam - i + 1)*binary_expo(i,MOD-2);
precalc[i] %= MOD;
}
for(ll i = N;i>=1;i--){
if(!(A[i] <= intervalos[v] && intervalos[v+1] <= B[i] )) continue;
dp[i][1] = 1;
for(ll j = i+1;j<=N;j++){
dp[i][1] += somatorio1[j];
}
dp[i][1] %= MOD;
dp[i][1] = (dp[i][1] * tam) % MOD;
for(ll k = 2;k<=vaiate;k++){
dp[i][k] = somatorio2[k-1];
}
dp2[i][v] = dp[i][1];
somatorio2[1] += dp[i][1];
somatorio2[1] %= MOD;
for(ll k = 2;k<=vaiate;k++){
dp[i][k] %= MOD;
dp[i][k] *= precalc[k];
dp[i][k] %= MOD;
dp2[i][v] += dp[i][k];
somatorio2[k] += dp[i][k];
somatorio2[k] %= MOD;
}
dp2[i][v] %= MOD;
tot += dp2[i][v];
tot %= MOD;
}
for(int i = 1;i<=N;i++){
somatorio1[i] += dp2[i][v];
somatorio1[i] %= MOD;
}
}
cout << tot << endl;
return 0;
}
