试题F:Fibonacci数列与黄金分割

import java.util.Scanner;

public class Main {
    public static long f(int n){
        if(n == 1 || n == 2){
            return 1 ;
        }else{
            long [] res = new long [n+1] ;
            res[1] = 1 ;
            res[2] = 1 ;
            for(int i=3; i<=n; i++){
                res[i] = res[i-1] + res[i-2] ;
            }
            return res[n] ;
        }
    }
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in) ;
        int n = input.nextInt();
        if(n <= 19)
        System.out.printf("%.8f", 1.0 * f(n)/f(n+1));
        else{
            System.out.println("0.61803399");
        }
    }
}