#include <bits/stdc++.h>
using namespace std;
const int N = 300;
const int INF = 1 << 29;
int a[9][N][N], b[N][N], c[N][N];
void multiply(int a[N][N], int b[N][N], int c[N][N], int n) {
  for (int i = 0; i < n; ++i) {
    for (int j = 0; j < n; ++j) {
      c[i][j] = -INF;
      for (int k = 0; k < n; ++k) {
        if (a[i][k] != -INF && b[k][j] != -INF) {
          c[i][j] = max(c[i][j], a[i][k] + b[k][j]);
        }
      }
    }
  }
}
void init(int a[N][N], int n) {
  for (int i = 0; i < n; ++i) {
    for (int j = 0; j < n; ++j) {
      a[i][j] = -INF;
    }
    a[i][i] = 0;
  }
}
int main() {
  int n, m;
  scanf("%d %d", &n, &m);
  init(a[0], n);
  while (m--) {
    int x, y, u, v;
    scanf("%d %d %d %d", &x, &y, &u, &v);
    --x;
    --y;
    a[0][x][y] = u;
    a[0][y][x] = v;
  }
  for (int k = 1; k <= 8; ++k) {
    multiply(a[k - 1], a[k - 1], a[k], n);
  }
  int ret = 0;
  init(b, n);
  for (int k = 8; k >= 0; --k) {
    multiply(b, a[k], c, n);
    bool found = false;
    for (int i = 0; i < n; ++i) {
      if (c[i][i] > 0) {
        found = true;
        break;
      }
    }
    if (!found) {
      ret += 1 << k;
      memcpy(b, c, sizeof(b));
    }
  }
  ret += 1;
  if (ret > n)
    puts("0");
  else
    printf("%d\n", ret);
  return 0;
}
