#include <bits/stdc++.h>
using namespace std;
using ll = long long;
ll MOD = 1e9 + 7;
const int mn = 1e3;
ll logpow(int a, int 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 choose(ll n, ll r) {
if (n < r)
return 0;
ll num = 1;
for (int i = 0; i < r; i++)
num = num * ((n - i) % MOD) % MOD;
return num * logpow(fac[r], MOD - 2) % MOD;
}
int 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);
}
vector<vector<array<ll, 3>>> vvi; // surplus, stage, multi
vvi.emplace_back(si.size());
for (int i = 0; i < n; i++) {
ll cur = 1;
for (int j = 0; j + 1 < sth.size(); j++) {
auto &[plus, stage, multi] = vvi[i][j];
ll befcur = cur;
cur += plus * (sth[j + 1] - sth[j]) % MOD;
cur %= MOD;
cur += choose((sth[j + 1] - sth[j]) + stage, stage + 1) * multi % MOD;
cur %= MOD;
if (sth[j] >= vpii[i].first && sth[j] <= vpii[i].second) {
if (stage == 0 && multi == 0) {
multi = befcur;
stage = 0;
} else {
plus += befcur;
plus %= MOD;
stage++;
}
}
}
vvi.push_back(vvi.back());
}
ll ans = 0;
for (int j = 0; j + 1 < sth.size(); j++) {
auto &[plus, stage, multi] = vvi.back()[j];
ans += plus * (sth[j + 1] - sth[j]) % MOD;
ans %= MOD;
ans += choose((sth[j + 1] - sth[j]) + stage, stage + 1) * multi % MOD;
ans %= MOD;
}
cout << ans << "\n";
}
