using System;
using System.Collections.Generic;
using System.IO;
class Solution {
    static void Main(String[] args) {
        /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution */
        int[] values = Array.ConvertAll(Console.ReadLine().Split(' '), Int32.Parse);
        int a = values[0], b = values[1], t = values[2];
        Console.WriteLine((0.5 * a * t + 0.5 * b * t) % (Math.Pow(10, 9) + 7));
        Console.ReadLine();
    }
}