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[] line = Array.ConvertAll(Console.ReadLine().Split(' '), Int32.Parse);

            double pp = (line[0] + line[1]) * 0.5 * line[2];

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