母牛的故事

题目：https://www.nowcoder.com/pat/2/problem/255

#include <iostream>
#include <algorithm>
using namespace std;

const int maxn = 60;
long long f[maxn];
void db(){
    f[1] = 1;
    f[2] = 2;
    f[3] = 3;
    f[4] = 4;
    f[5] = 6;
    for (int i = 6; i < maxn; i++){
        f[i] = f[i - 1] + f[i - 3];
    }
}

int main(){
    std::ios::sync_with_stdio(false);
    int n;
    db();
    while (cin >> n){
        cout << f[n] << endl;
    }
    //system("pause");
    return  0;
}