using System;
using System.Numerics;

public class Hello
{
    private  const int MOD = 1000000007;
    public static void Main()
    {
        BigInteger ans = 0;
        var n = int.Parse(Console.ReadLine().Trim());
        for (int i = 0; i < n; i++)
        {
            string[] line = Console.ReadLine().Trim().Split(' ');
            BigInteger c = BigInteger.Parse(line[0]);
            BigInteger d = BigInteger.Parse(line[1]);
            ans  += ((c + 1) / 2L) * d;
        }
        ans %= MOD;
        Console.WriteLine(ans);
    }
}