#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll, ll> pll;
typedef pair<int, int> pii;
#define all(x) (x).begin(),(x).end()
#define X first
#define Y second
#define sep ' '
#define endl '\n'
#define SZ(x) ll(x.size())
const ll MAXN = 1000 + 10;
const ll LOG = 22;
const ll INF = 8e18;
const ll MOD = 1e9 + 7; //998244353; //1e9 + 9;
ll n , L[MAXN] , R[MAXN] , dp[MAXN][MAXN] , ps[MAXN] , inv[MAXN];
vector<int> compress = {0};
ll poww(ll a , ll b){
ll ans = 1;
for( ; b ; b /= 2 , a = a * a % MOD) if(b & 1) ans = ans * a % MOD;
return ans;
}
int main() {
ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
for(int i = 1 ; i < MAXN ; i++) inv[i] = poww(i , MOD - 2);
// for(int i = 1 ; i <= 5 ; i++) cout << i << sep << inv[i] << endl;
cin >> n;
for(int i = 1 ; i <= n ; i++){
cin >> L[i] >> R[i]; R[i]++;
compress.push_back(L[i]);
compress.push_back(R[i]);
}
sort(all(compress));
compress.resize(unique(all(compress)) - compress.begin());
dp[0][0] = 1; fill(ps , ps + MAXN , 1);
for(int i = 1 ; i <= n ; i++){
L[i] = lower_bound(all(compress) , L[i]) - compress.begin();
R[i] = lower_bound(all(compress) , R[i]) - compress.begin();
for(int j = L[i] ; j < R[i] ; j++){
int len = compress[j + 1] - compress[j];
for(int k = n ; k >= 2 ; k--){
dp[j][k] = (dp[j][k] + dp[j][k - 1] * (len - k + 1) % MOD * inv[k]) % MOD;
}
dp[j][1] = (dp[j][1] + ps[j - 1] * len) % MOD;
}
ps[0] = dp[0][0];
for(int j = 1 ; j < MAXN ; j++){
ps[j] = ps[j - 1];
for(int k = 0 ; k <= n ; k++){
ps[j] = (ps[j] + dp[j][k]);
}
ps[j] %= MOD;
}
}
cout << (ps[MAXN - 1] + MOD - 1) % MOD << endl;
return 0;
}
/*
*/
