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;
}