using System;

public class Program

{

    public static void Main()

    {

​

double a, b, c, p, S;

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

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

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

        p=(a+b+c)/2;

        S=Math.Sqrt(p*(p-a)*(p-b)*(p-c));

        Console.WriteLine("S="+S);

    }

}