#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll mod = 1e9 + 7;
ll pref[505][1005], ia[505];
ll pwr(ll a, ll b){
ll ans = 1;
while (b){
if (b & 1) ans = ans * a % mod;
a = a * a % mod;
b >>= 1;
}
return ans;
}
ll inv(ll a){
return pwr(a, mod - 2);
}
int main(){
ios_base::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
int nums; cin >> nums;
for (int i = 1; i <= nums; i++) ia[i] = inv(i);
vector<ll> av(nums + 1), bv(nums + 1), disc; disc.push_back(-1);
for (int i = 1; i <= nums; i++){
ll a, b; cin >> a >> b; b++;
av[i] = a; bv[i] = b;
disc.push_back(a); disc.push_back(b);
}
sort(disc.begin(), disc.end());
disc.resize(distance(disc.begin(), unique(disc.begin(), disc.end())));
int segs = disc.size() - 2;
for (int j = 0; j <= segs; j++) pref[0][j] = 1;
ll ans = 0;
for (int i = 1; i <= nums; i++)
for (int j = 1; j <= segs; j++){
ll dpv = 0, len = disc[j + 1] - disc[j];
if (av[i] <= disc[j] && bv[i] >= disc[j + 1]){
ll cv = len; int cnt = 1;
for (int k = i - 1; k >= 0; k--){
dpv = (dpv + pref[k][j - 1] * cv % mod) % mod;
if (av[k] <= disc[j] && bv[k] >= disc[j + 1]){
cnt++; cv = cv * (len + cnt - 1) % mod * ia[cnt] % mod;
}
}
}
pref[i][j] = (pref[i][j - 1] + dpv) % mod;
ans = (ans + dpv) % mod;
}
cout << ans;
}
