double power(double n){
  if (n == 1) {
    return 1;
  }     
  return (1 / power( n ))  ;
}

/*
  计算 1 + 2 + 3 ... + n 
*/
public class Test{

  public static void main(String[] args){
    System.out.println(recursion(5));
  }


  private static int recursion(int n){
    if(n==1){
      return 1;
    }
    else{
      return (n + recursion(n-1));
    }
  }

}