#include <cstdio>
#include <cmath>
#include <cstring>
#include <iostream>
#include <iomanip>
#include <sstream>
#include <map>
#include <set>
#include <array>
#include <queue>
#include <string>
#include <vector>
#include <numeric>
#include <algorithm>
#include <functional>
#define MOD 1000000007
#define INF 11234567890
#define in std::cin
#define out std::cout
#define rep(i,N) for(LL i=0;i<N;++i)
typedef long long int LL;
typedef std::pair<int, int> P;

LL N, C[112345], D[112345];
LL ans;

int main()
{
	in >> N;
	rep(i, N) { in >> C[i] >> D[i]; }

	rep(i, N)
	{
		if (C[i] % 2 == 1)
		{
			ans += (C[i] / 2 + 1) * D[i];
		}
		else
		{
			ans += (C[i] / 2) * D[i];
		}
		ans %= MOD;
	}

	out << ans << std::endl;
	return 0;
}