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]));
}