using System;

public class Hello
{
    static void Main()
    {
        string[] line = Console.ReadLine().Trim().Split(' ');
        var a = int.Parse(line[0]);
        var b = int.Parse(line[1]);
        var c = decimal.Parse(line[2]);
        var ans = (a + b) * (c + 1);
        Console.WriteLine((int)ans);
    }
}