看到可以选择一次或两次就要想到斐波那契数列，直接动态规划就行

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int p = 0, q = 1, r = 1;
        while (n-- > 0) {
            r = p + q;
            p = q;
            q = r;
        }
        System.out.println(r);
    }
}