动态规划

#include<iostream>
using namespace std;

int n, dp[55];
int main() {

    cin >> n;
    dp[0] = 1, dp[1] = 1, dp[2] = 1;
    for( int i = 3; i <= n; i++ )
        dp[i] = dp[i - 1] + dp[i - 3]; //状态转移方程

    cout << dp[n];
    
}