using System;
using System.Collections.Generic;
using System.IO;
class Solution {
    static void Main(String[] args) {
        var a = Array.ConvertAll(Console.ReadLine().Split(' '), int.Parse);

        var ms = a[2];
        var f1 = a[0];
        var f2 = a[1];

        double res = 0;

        double cells = 1L;
        for (var i = 1; i <= ms; i++)
        {
            cells = ((0.5f * f1 * cells) + (0.5f * f2 * cells));
            res += cells % 1000000007;
        }

        Console.WriteLine(res);
    }
}