using System;

public class Program

{

    public static void Main()

    {

        double a, ha; 

​

Console.Write("a = "); 

​

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

​

Console.Write("ha = "); 

​

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

​

double s = a * ha/2; 

​

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

    }

}

​

​