#include <bits/stdc++.h>
using namespace std;
const int P = 1e9 + 7, INF = 0x3f3f3f3f;
long long gcd(long long a, long long b) { return b ? gcd(b, a % b) : a; }
long long qpow(long long a, long long n) {
  long long r = 1 % P;
  for (a %= P; n; a = a * a % P, n >>= 1)
    if (n & 1) r = r * a % P;
  return r;
}
long long inv(long long first) {
  return first <= 1 ? 1 : inv(P % first) * (P - P / first) % P;
}
inline int rd() {
  int first = 0;
  char p = getchar();
  while (p < '0' || p > '9') p = getchar();
  while (p >= '0' && p <= '9') first = first * 10 + p - '0', p = getchar();
  return first;
}
const int N = 1e6 + 10;
int n, m, vis[N], d[N];
struct _ {
  int to, w, vis;
};
vector<_> g[N];
struct __ {
  int id, w;
  bool operator<(const __ &rhs) const { return w > rhs.w; }
};
priority_queue<__> q;
void dfs(int first, int w, int dd) {
  if (vis[first]) return;
  vis[first] = 1;
  if (d[first] > dd) q.push({first, d[first] = dd});
  for (_ &e : g[first])
    if (e.w == w) {
      if (e.vis) continue;
      e.vis = 1;
      dfs(e.to, w, dd);
    }
}
int main() {
  cin >> n >> m;
  while (m--) {
    int p, q, c;
    cin >> p >> q >> c;
    g[p].push_back({q, c});
    g[q].push_back({p, c});
  }
  memset(d, 0x3f, sizeof d);
  q.push({1, d[1] = 0});
  while (q.size()) {
    int u = q.top().id;
    q.pop();
    if (vis[u]) continue;
    vis[u] = 1;
    for (auto e : g[u]) dfs(e.to, e.w, d[u] + 1);
  }
  printf("%d\n", vis[n] ? d[n] : -1);
}
