class Main {
  public static void main(String[] args) {
    System.out.println(sin(0.1, 10));
  }

  public static int factorial(int n){
    if(n <= 0)
      return 1;

    return factorial(n - 1) * n;
  }

  public static double sin(double x, int n){
    double ret = 0.0;

    if(n < 1)
      return 1;

    for(int i = 0; i <= n; i++)
      ret += Math.pow(-1, i) * Math.pow(x, 1 + (2 * i))
        / factorial(1 + (2 * i));

    return ret;
  }
}