#include <bits/stdc++.h>

using namespace std;

#define DEBUG(x) cerr<<#x<<": "<<x<<endl;
#define DEBUG_VEC(v) cerr<<#v<<":";for(int i=0;i<v.size();i++) cerr<<" "<<v[i]; cerr<<endl

typedef long long ll;
#define vi vector<int>
#define vl vector<ll>
#define vii vector< vector<int> >
#define vll vector< vector<ll> >
#define vs vector<string>
#define pii pair<int,int>
#define pis pair<int,string>
#define psi pair<string,int>
#define pll pair<ll,ll>
template<class S, class T> pair<S, T> operator+(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first + t.first, s.second + t.second); }
template<class S, class T> pair<S, T> operator-(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first - t.first, s.second - t.second); }
template<class S, class T> ostream& operator<<(ostream& os, pair<S, T> p) { os << "(" << p.first << ", " << p.second << ")"; return os; }
#define X first
#define Y second
#define rep(i,n) for(int i=0;i<(n);i++)
#define rep1(i,n) for(int i=1;i<=(n);i++)
#define rrep(i,n) for(int i=(n)-1;i>=0;i--)
#define rrep1(i,n) for(int i=(n);i>0;i--)
#define REP(i,a,b) for(int i=a;i<b;i++)
#define in(x, a, b) (a <= x && x < b)
#define all(c) c.begin(),c.end()
template<class T> bool chmax(T &a, const T &b) { if (a<b) { a = b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a = b; return 1; } return 0; }
#define UNIQUE(v) v.erase(std::unique(v.begin(), v.end()), v.end());
const ll inf = 1000000001;
const ll INF = 1e18;
const ll MOD = 1000000007;
//const ll MOD = 998244353;
const double pi = 3.14159265358979323846;
#define Sp(p) cout<<setprecision(15)<< fixed<<p<<endl;
int dx[4] = { 1,0, -1,0 }, dy[4] = { 0,1,0,-1 };
int dx2[8] = { 1,1,0,-1,-1,-1,0,1 }, dy2[8] = { 0,1,1,1,0,-1,-1,-1 };
#define fio() cin.tie(0); ios::sync_with_stdio(false);
//#define mp make_pair

int main() {
  int n, m;
  cin >> n >> m;
  vector<pair<pii, int> > g;
  vector<set<int> > st(n);
  rep (i, m) {
    int u, v, c;
    cin >> u >> v >> c;
    u--; v--;
    g.push_back({pii(u, v), c});
    st[u].insert(c);
    st[v].insert(c);
  }
  vector<pii> eki;
  map<pii, int> idx;
  rep (i, n) {
    eki.push_back(pii(i, 0));
    idx[pii(i, 0)] = i;
  }
  int zen = n;
  rep (i, n) {
    for (auto itr = st[i].begin(); itr != st[i].end(); itr++) {
      int c = *itr;
      pii p = pii(i, c);
      eki.push_back(p);
      idx[p] = zen++;
    }
  }
  vector<vector<pii> > G(zen);
  rep (i, n) {
    int u = i;
    for (auto itr = st[i].begin(); itr != st[i].end(); itr++) {
      int c = *itr;
      pii p = pii(i, c);
      int v = idx[p];
      G[u].push_back(pii(1, v));
      G[v].push_back(pii(0, u));
    }
  }
  rep (i, m) {
    int u = g[i].first.first, v = g[i].first.second, c = g[i].second;
    int uu = idx[pii(u, c)], vv = idx[pii(v, c)];
    G[uu].push_back(pii(0, vv));
    G[vv].push_back(pii(0, uu));
  }
  //DEBUG_VEC(eki);
  vl d(zen, INF);
  priority_queue<pll, vector<pll>, greater<pll> > pq;
  d[0]=0;
  pq.push(make_pair(0, 0));
  while(!pq.empty()){
    pll f=pq.top();
    pq.pop();
    int u=f.second;
    if(d[u]<f.first){
      continue;
    }
    for (int i = 0; i < G[u].size(); i++) {
      int v=G[u][i].second;
      if (d[v] > d[u] + G[u][i].first) {
        d[v] = d[u] + G[u][i].first;
        pq.push(make_pair(d[v], v));
      }
    }
  }
  cout << (d[n - 1] >= INF / 2 ? -1 : d[n - 1]) << endl;
}


Measured memory_bytes: 101036