题解

#include<bits/stdc++.h>
using namespace std;
int main(){
	long long a[81] = {0,1,2,4,7};
	int n;
	cin >> n;
	for(int i=5;i<=n;i++)a[i] = a[i-1]+a[i-2]+a[i-4];
	cout << a[n];
	return 0;
}