public class MyClass {
  public static void main(String[] args) {
    System.out.println(Math.acos(0.64));
    System.out.println(Math.acos(-0.4));
    System.out.println(Math.acos(0));
    System.out.println(Math.acos(1));
    System.out.println(Math.acos(-1));
    System.out.println(Math.acos(2));
  }
}