using System;

public class Program

{

    public static void Main()

    {

        int a = 1;

        double b = 1;

        double[] c = { 1, 1 };

        Console.WriteLine(Math.Acos(a));

        Console.WriteLine(Math.Acos(b));        

        Console.WriteLine(Math.Acos(c[0]));

        Console.WriteLine(Math.Acos(c[1]));

    }

}