#include<bits/stdc++.h>
#include<fstream>
using namespace std;
ifstream fin("FEEDING.INP");
ofstream fout("FEEDING.OUT");
#define sz(a) (int)a.size()
#define ll long long
#define pb push_back
#define forr(i, a, b) for(int i = a; i < b; i++)
#define dorr(i, a, b) for(int i = a; i >= b; i--)
#define ld long double
#define vt vector
#include<fstream>
#define fi first
#define se second
#define pll pair<ll, ll>
#define pii pair<int, int>
const ld PI = 3.14159265359;
using u128 = __uint128_t;
const int x[4] = {1, -1, 0, 0};
const int y[4] = {0, 0, 1, -1};
const ll mod = 1e9 + 7, inf = 1e16;
const int mxn = 3e5 + 5;
int n;
ll l[505], r[505], inv[505], dp[1005][505];
ll pw(ll a, ll b){
ll res = 1;
for(;b;b >>= 1){
if(b & 1){
res = (res * a) % mod;
}
a = (a * a) % mod;
}
return(res);
}
signed main()
{
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
cin >> n;
vt<int>comp;
for(int i = 1; i <= n; i++){
cin >> l[i] >> r[i];
inv[i] = pw(i, mod - 2);
comp.pb(l[i]); comp.pb(r[i] + 1);
}
comp.pb(0);
sort(comp.begin(), comp.end()); comp.resize(unique(comp.begin(), comp.end()) - comp.begin());
for(int i = 0; i <= n; i++){
dp[0][i] = 1;
}
for(int i = 1; i < sz(comp) - 1; i++){
for(int j = 0; j <= n; j++){
dp[i][j] = dp[i - 1][j];
ll ways = 1, cnt = 0;
for(int k = j; k >= 1; k--){
if(l[k] <= comp[i] && comp[i + 1] - 1 <= r[k]){
cnt++;
ll sus = ((comp[i + 1] - comp[i] + cnt - 1) * inv[cnt]) % mod;
ways = (ways * sus) % mod;
//cout << sus << " ";
dp[i][j] = (dp[i][j] + dp[i - 1][k - 1] * ways) % mod;
}
}
}
}
cout << (dp[sz(comp) - 2][n] - 1 + mod) % mod;
return(0);
}
