MLE 啊！！！

哪位大佬帮忙看一下我的代码为什么会MLE！

#include <map>
#include <set>
#include <list>
#include <cmath>
#include <queue>
#include <stack>
#include <cstdio>
#include <vector>
#include <cstdlib>
#include <cstring>
#include <iomanip>
#include <iterator>
#include <iostream>
#include <algorithm>

using namespace std;

typedef long long LL;

const int N = 5e3 + 5;
const int MOD = 1e9 + 7;
const int INF = 0x3f3f3f3f;

LL n, len = 1, f[N][N];

void func(int x) {
    for (LL i = 1; i <= len; ++i) {
        f[x][i] = f[x - 1][i] + f[x - 2][i];
    }
    for (LL i = 1; i <= len; ++i) {
        if (f[x][i] > 9) {
            f[x][i + 1] += f[x][i] / 10;
            f[x][i] %= 10;
        }
    }
    if (f[x][len + 1]) {
        ++len;
    }
}

int main(void) {
    cin >> n;
    f[1][1] = 1;
    f[2][1] = 2;
    for (LL i = 3; i <= n; ++i) {
        func(i);
    }
    for (LL i = len; i; --i) {
        cout << f[n][i];
    }
    cout << endl;

    return 0;
}