#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

ll mod = 1e9+7;

ll mul(ll a, ll b) {
	a %= mod;
	b %= mod;
	return a * b % mod;
}
ll add(ll a, ll b) {
	a %= mod;
	b %= mod;
	return (a + b) % mod;
}

int main() {
	ll N; cin >> N;
	ll ans = 0;
	for (int i = 0; i < N; ++i) {
		ll c, d; cin >> c >> d;
		c = (c + 1) / 2;
		ans = add(ans, mul(c, d));
	}
	cout << ans << endl;
}