using System;
public class Triangle{
    private static void Main(){
        String[] input = Console.ReadLine().Split(' ');
        double a= double.Parse(input[0]);
        double b= double.Parse(input[1]);
        double c= double.Parse(input[2]);
        double p =(a+b+c)*0.5;
        Console.WriteLine(Math.Round(Math.Sqrt(p*(p-a)*(p-b)*(p-c)), 1));
    }
}