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 */
        double a=Console.Read();
        double b=Console.Read();
        double t=Console.Read();
        double cells=0;
        cells=(0.5*a*t)+(0.5*b*t);
        cells=cells % ((10^9) + 7);
        Console.Write(cells);
    }
}