05.TrapeziodArea

using System;

class Program
{
    static void Main()
    {
        var b1 = double.Parse(Console.ReadLine());
        var b2 = double.Parse(Console.ReadLine());
        var h = double.Parse(Console.ReadLine());

        var area = (b1 + b2) * h / 2;
        Console.WriteLine("Trapezoid area = {0}", area);
    }
}