#include <bits/stdc++.h>
using namespace std;
const int N = 310;
const int INF = 0x3f3f3f3f;
const int mod = 1e9 + 7;
const double eps = 1e-6;
const double PI = acos(-1.0);
int n, m, ans = 1;
int d[10][N][N];
int f[N][N], tmp[N][N];
int lg[N];
void init() {
  for (int i = 1; i <= n; i++) {
    lg[i] = lg[i - 1] + (1 << lg[i - 1] == i);
  }
  memset(d, -INF, sizeof d);
  memset(f, -INF, sizeof f);
  for (int i = 1; i <= n; i++) {
    d[0][i][i] = 0;
    f[i][i] = 0;
  }
}
void floyd() {
  for (int s = 1; s <= lg[n]; s++) {
    for (int k = 1; k <= n; k++) {
      for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= n; j++) {
          d[s][i][j] = max(d[s][i][j], d[s - 1][i][k] + d[s - 1][k][j]);
        }
      }
    }
  }
}
void solve() {
  cin >> n >> m;
  init();
  while (m--) {
    int u, v;
    cin >> u >> v;
    cin >> d[0][u][v] >> d[0][v][u];
  }
  floyd();
  for (int s = 1; s <= lg[n]; s++) {
    for (int k = 1; k <= n; k++) {
      for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= n; j++) {
          d[s][i][j] = max(d[s][i][j], d[s - 1][i][k] + d[s - 1][k][j]);
        }
      }
    }
  }
  for (int s = lg[n]; ~s; s--) {
    memset(tmp, -INF, sizeof tmp);
    for (int k = 1; k <= n; k++) {
      for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= n; j++) {
          tmp[i][j] = max(tmp[i][j], f[i][k] + d[s][k][j]);
        }
      }
    }
    bool flag = 0;
    for (int i = 1; i <= n; i++) {
      if (tmp[i][i] > 0) {
        flag = 1;
        break;
      }
    }
    if (flag)
      continue;
    else {
      ans += (1 << s);
      memcpy(f, tmp, sizeof tmp);
    }
  }
  if (ans > n)
    cout << "0\n";
  else
    cout << ans << "\n";
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  solve();
  return 0;
}
