剑指OFFER----跳台阶变形

#include<iostream>  
#include<cstring>  
#include<cstdio>  
using namespace std;
long long _cuopai[100];
long long func(int x)
{
	if (_cuopai[x]) return _cuopai[x];
	if (x == 1) return 1;
	if (x == 2) return 2;
	if (x == 3) return 3;
	return _cuopai[x] = func(x - 1) + func(x - 3);
}
int main()
{
	int a;
	cin >> a;
	cout << func(a) << endl;
	return 0;
}