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

namespace Trapec
{
    public class Trapec
    {
        public double a;
        public double b;
        public double h;

        public void Input()
        {
            a = double.Parse(Console.ReadLine());
            b = double.Parse(Console.ReadLine());
            h = double.Parse(Console.ReadLine());
        }
        public void Output()
        {
            Console.WriteLine("a: " +a);
            Console.WriteLine("b: " + b);
            Console.WriteLine("h: " + h);
        }
        public Trapec()
        {
            a = 0.0;
            b = 0.0;
            h = 0.0;
        }
        public void S()
        {
            Console.WriteLine("S = "+(a+b)*h/2);
        }
    }
}