using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication3
{
    class Program
    {
        static void Main(string[] args)
        {
            string s1 = Console.ReadLine();
            string[] s1_temp = s1.Split(' ');
            int[] s1_f = Array.ConvertAll(s1_temp, Int32.Parse);
            int a = s1_f[0];
            int b = s1_f[1];
            int t = s1_f[2];
            double size = 0;
            for(int i=0; i<t; i++)
            {
                size += (0.5 * a) + (0.5 * b);
            }

            size = size % (Math.Pow(10, 9) + 7);
            Console.WriteLine(size);
        }
    }
}