using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Лице на трапец");

        Console.Write("a=");

    double a = double.Parse(Console.ReadLine());

​

        Console.Write("b=");

    double b = double.Parse(Console.ReadLine());

​

        Console.Write("h=");

    double h = double.Parse(Console.ReadLine());

​

        double s = (a+b)*h/2;

        Console.Write("s=" + s);

    }

}