#include <bits/stdc++.h>
using namespace std;
using ll = long long;
ll MOD = 1e9 + 7;
const int mn = 501, msth = 1001;
ll logpow(ll a, ll b) {
if (b == 0)
return 1;
if (b == 1)
return a;
ll x = logpow(a, b / 2);
if (b % 2 == 1)
return x * x % MOD * a % MOD;
return x * x % MOD;
}
vector<ll> fac;
ll precomp[msth][mn] = {}, dp[msth][mn] = {}, prec[mn][mn] = {};
signed main() {
int n;
cin >> n;
vector<pair<int, int>> vpii(n);
for (auto &a : vpii)
cin >> a.first >> a.second;
fac = vector<ll>(mn);
fac[0] = 1;
for (int i = 1; i < mn; i++)
fac[i] = fac[i - 1] * i % MOD;
set<int> si;
for (auto [a, b] : vpii)
si.insert(a), si.insert(b + 1);
vector<ll> sth;
for (auto a : si) {
sth.push_back(a);
}
for (int i = 0; i <= n; i++)
for (int j = 0; j <= i; j++)
prec[i][j] = fac[i] * logpow(fac[j], MOD - 2) % MOD *
logpow(fac[i - j], MOD - 2) % MOD;
vector<int> helper(n + 1);
for (int i = 0; i + 1 < sth.size(); i++) {
ll cur = sth[i + 1] - sth[i];
for (int j = 1; j <= n; j++) {
helper[j] = cur * logpow(fac[j], MOD - 2) % MOD;
cur = cur * (sth[i + 1] - sth[i] - j) % MOD;
}
for (int j = 1; j <= n; j++) {
for (int k = 0; k + 1 <= j && k + 1 <= sth[i + 1] - sth[i]; k++) {
precomp[i][j] += prec[j - 1][k] * helper[k + 1] % MOD;
precomp[i][j] %= MOD;
}
}
}
int ans = 0;
dp[0][0] = 1;
for (int i = 0; i + 1 < sth.size(); i++) {
for (int j = 0; j < n; j++) {
dp[i + 1][j] += dp[i][j];
dp[i + 1][j] %= MOD;
int ct = 0;
for (int k = j; k < n; k++) {
if (sth[i] >= vpii[k].first && vpii[k].second + 1 >= sth[i + 1]) {
ct++;
dp[i + 1][k + 1] += dp[i][j] * precomp[i][ct] % MOD;
dp[i + 1][k + 1] %= MOD;
ans += dp[i][j] * precomp[i][ct] % MOD;
ans %= MOD;
}
}
}
}
cout << ans << "\n";
}
