using System;

public class Program

{

    public static double S(double a)

        {return a;}

    public static void Main()

    {

        double x;

        Console.WriteLine("1va strana");

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

        double y;

        Console.WriteLine("2ra strana");

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

        double z;

        Console.WriteLine("3ta strana");

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

        double p = (x + y + z) /2;

        double s = Math.Sqrt( p * (p - x) * (p - y) * (p - z));

        Console.WriteLine("liceto e " + S(s));

        return;

    }

}