#include <bits/stdc++.h>
using namespace std;
const int N = 505;
const long long inf = 1e18;
inline int read() {
  int x = 0;
  char c = getchar();
  while (!isdigit(c)) c = getchar();
  while (isdigit(c)) x = (x << 3) + (x << 1) + (c ^ 48), c = getchar();
  return x;
}
int n, m, now;
long long ans, Pow[100];
bitset<N> f[2][64][N], g, tmp;
int main() {
  n = read();
  m = read();
  int u, v, w;
  for (int i = 1; i <= m; ++i) {
    u = read();
    v = read();
    w = read();
    f[w][0][u][v] = 1;
  }
  for (int i = 1; i <= 60; ++i)
    for (int u = 1; u <= n; ++u)
      for (int v = 1; v <= n; ++v) {
        if (f[0][i - 1][u][v]) f[0][i][u] |= f[1][i - 1][v];
        if (f[1][i - 1][u][v]) f[1][i][u] |= f[0][i - 1][v];
      }
  if (f[0][60][1].count()) {
    puts("-1");
    return 0;
  }
  now = 0;
  tmp[1] = 1;
  Pow[0] = 1;
  for (int i = 1; i <= 60; ++i) Pow[i] = Pow[i - 1] << 1;
  for (int i = 60; i >= 0; --i) {
    g.reset();
    for (int j = 1; j <= n; ++j)
      if (tmp[j]) g |= f[now][i][j];
    if (g.count()) {
      now ^= 1;
      tmp = g;
      ans += Pow[i];
    }
  }
  if (ans > inf)
    puts("-1");
  else
    printf("%lld", ans);
}
