#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <map>
#include <set>
#include <stdio.h>
#include <cstring>
#include <queue>
#include <stack>
#include <functional>
#include <math.h>
#include <iomanip>
using namespace std;
#define Would
#define you
const int INF = 999999999;
const int MOD = 1e9 + 7;

long long n, a, b, ans;
int main() {
	cin >> n;
	for (int i = 0; i < n; ++i) {
		cin >> a >> b;
		ans += b * (a / 2 + a % 2);
		ans %= MOD;
	}
	cout << ans % MOD << endl;
}