题解

#include <bits/stdc++.h>
using namespace std;
int main(){
	int n;
	cin>>n;
	int a[31] = {0,1,2,4,7,12};
	for (int i=5;i<=n;i++) a[i] = a[i-1]+a[i-2]+a[i-4];
	cout<<a[n];
	return 0;
}