记忆化搜索WA了几个点，请大佬帮忙看看，代码简洁

#include<iostream>
#include<cstring>

using namespace std;
const int N = 5e3 + 10;
long long f[N];   //记忆化数组！
int n;

int dfs (int u)
{   
    if (u>n) return 0;    
    if (f[u]!=-1) return f[u];
    if (u==n) return f[u]=1;

    f[u] = dfs(u+1) + dfs(u+2);
    return f[u];
}   

int main()
{
    cin >> n;
    memset (f, -1, sizeof(f));

    cout << dfs (0);

    return 0;
}