using System;
using System.Collections.Generic;
using System.Linq;

class Magatro
{
    static void Main()
    {
        int mod = 1000000007;
        int N = int.Parse(Console.ReadLine());
        long[] C = new long[N];
        long[] D = new long[N];
        for(int i = 0; i < N; i++)
        {
            string[] s = Console.ReadLine().Split(' ');
            long w = long.Parse(s[0]);
            long q=w%2==0?w/2:w / 2+1;
            D[i] = (long.Parse(s[1])*q)%mod;
        }
        long ans = 0;
        for(int i = 0; i < N; i++)
        {
            ans = (ans + D[i]) % mod;
        }
        Console.WriteLine(ans);
    }
}