清雨的自助餐(斐波那契数列的应用)

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner cin = new Scanner(System.in);
        int n = cin.nextInt();
        cin.close();
        System.out.println(fibonacci(n));
    }

    private static long fibonacci(int n) {
        long y1 = 2, y2 = 3, y3 = 5, y = 0;
        for (int i = 4; i <= n; ++i) {
            y = y3 + y2;
            y2 = y3;
            y3 = y;
        }
        if (n == 1)
            return y1;
        if (n == 2)
            return y2;
        if (n == 3)
            return y3;
        return y;
    }
}