90pts暴力搜索+剪枝，求证复杂度，为什么能拿90分？（我一开始以为是30）

TLE on #9 是我的复杂度错误，还是写错了？

谢大佬！

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <cmath>
using namespace std;

const int NR = 1010;
int n, m;

struct edge
{
	int nxt, to;
	int c, f;
}e[NR * 2];

int head[NR], cnt;

void add(int x, int y, int c, int f)
{
	e[++cnt] = (edge){head[x], y, c, f};
	head[x] = cnt;
}

int cn[NR], fn[NR];
int vis[NR];
long long ans = 0;

void dfs(int x, long long c, long long f)
{
	if (c != 0 && ans > (long long)floor(1.0 * f / c * 1e6)) return;
	vis[x] = 1;
	if (x == n)
	{
		ans = max(ans, (long long)floor(1.0 * f / c * 1e6));
		vis[x] = 0;
		return;
	}
	for (int i = head[x]; i; i = e[i].nxt)
	{
		int y = e[i].to;
		if (!vis[y])
		{
			dfs(y, c + e[i].c, min(f, 1ll * e[i].f));
		}
	}
	vis[x] = 0;
}

int main()
{
	scanf("%d%d", &n, &m);
	for (int i = 1; i <= m; i ++)
	{
		int a, b, c, f;
		scanf("%d%d%d%d", &a, &b, &c, &f);
		add(a, b, c, f);
		add(b, a, c, f);
	}
	dfs(1, 0, 1e9);
	printf("%lld\n", ans);
	return 0;
}