HDU 2018 母牛的故事

#include <bits/stdc++.h>

using namespace std;

const int maxn=1e5+10;

int A(int x)
{
    if(x<=4)
        return x;
    else
        return A(x-1)+A(x-3);
}

int main()
{
    int n;
    while(~scanf("%d",&n))
    {
        if(n==0)
            break;
        else
            printf("%d\n",A(n));
    }
    return 0;
}