#include <bits/stdc++.h>
#define FOR(v, a, b) for(int v = (a); v < (b); ++v)
#define FORE(v, a, b) for(int v = (a); v <= (b); ++v)
#define REP(v, n) FOR(v, 0, n)
#define REPE(v, n) FORE(v, 0, n)
#define REV(v, a, b) for(int v = (a); v >= (b); --v)
#define ALL(x) (x).begin(), (x).end()
#define ITR(it, c) for(auto it = (c).begin(); it != (c).end(); ++it)
#define RITR(it, c) for(auto it = (c).rbegin(); it != (c).rend(); ++it)
#define EXIST(c,x) ((c).find(x) != (c).end())
#define LLI long long int
#define fst first
#define snd second

#ifdef DEBUG
#include <misc/C++/Debug.cpp>
#else
#define dump(x) ((void)0)
#endif

#define gcd __gcd

using namespace std;
template <class T> constexpr T lcm(T m, T n){return m/gcd(m,n)*n;}

template <typename I> void join(ostream &ost, I s, I t, string d=" "){for(auto i=s; i!=t; ++i){if(i!=s)ost<<d; ost<<*i;}ost<<endl;}
template <typename T> istream& operator>>(istream &is, vector<T> &v){for(auto &a : v) is >> a; return is;}
template <typename T, typename U> istream& operator>>(istream &is, pair<T,U> &p){is >> p.first >> p.second; return is;}

template <typename T, typename U> bool chmin(T &a, const U &b){return (a>b ? a=b, true : false);}
template <typename T, typename U> bool chmax(T &a, const U &b){return (a<b ? a=b, true : false);}
template <typename T, size_t N, typename U> void fill_array(T (&a)[N], const U &v){fill((U*)a, (U*)(a+N), v);}

template <typename Cost = int> class Edge{
public:
  int from,to;
  Cost cost;
  Edge() {}
  Edge(int to, Cost cost): to(to), cost(cost){}
  Edge(int from, int to, Cost cost): from(from), to(to), cost(cost){}

  Edge rev() const {return Edge(to,from,cost);}
  
  static bool cmp_to_lt(const Edge &e1, const Edge &e2){return e1.to < e2.to;}
  static bool cmp_cost_lt(const Edge &e1, const Edge &e2){return e1.cost < e2.cost;}
  static bool cmp_to_gt(const Edge &e1, const Edge &e2){return e1.to > e2.to;}
  static bool cmp_cost_gt(const Edge &e1, const Edge &e2){return e1.cost > e2.cost;}
  friend ostream& operator<<(ostream &os, const Edge &e){
    os << "(FROM: " << e.from << "," << "TO: " << e.to << "," << "COST: " << e.cost << ")";
    return os;
  }
};

template <typename T> using Graph = vector<vector<Edge<T>>>;

template <typename T>
vector<T> dijkstra(Graph<T> &graph, int src){
  int n = graph.size();
  vector<T> cost(n, -1);
  vector<bool> check(n, false);
  priority_queue<pair<T,int>, vector<pair<T,int>>, greater<pair<T,int>>> pq;

  cost[src] = 0;
  pq.push(make_pair(0,src));

  while(!pq.empty()){
    int i; T d;
    tie(d,i) = pq.top(); pq.pop();

    if(check[i]) continue;
    check[i] = true;

    for(auto &e : graph[i]){
      if(cost[e.to] < 0){
	cost[e.to] = d + e.cost;
	pq.push(make_pair(cost[e.to], e.to));
      }else{
	if(cost[e.to] > d+e.cost){
	  cost[e.to] = min(cost[e.to], d + e.cost);
	  if(!check[e.to]) pq.push(make_pair(cost[e.to], e.to));
	}
      }
    }
  }
  
  return cost;
}



int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);

  int N,M;
  while(cin >> N >> M){
    vector<int> p(M), q(M), c(M);
    REP(i,M){
      cin >> p[i] >> q[i] >> c[i];
      --p[i], --q[i];
    }
    
    vector<map<int,int>> a(N);
    vector<set<int>> cs(N);

    REP(i,M){
      cs[p[i]].insert(c[i]);
      cs[q[i]].insert(c[i]);
    }

    int k = N;
    REP(i,N){
      for(auto j : cs[i]){
	a[i][j] = k;
	++k;
      }
    }

    Graph<int> g(k);
    
    
    REP(i,N){
      for(auto &kv : a[i]){
	g[i].push_back(Edge<int>(i, kv.snd, 1));
	g[kv.snd].push_back(Edge<int>(kv.snd, i, 0));
      }
    }

    REP(i,M){
      g[a[p[i]][c[i]]].push_back(Edge<int>(a[p[i]][c[i]], a[q[i]][c[i]], 0));
      g[a[q[i]][c[i]]].push_back(Edge<int>(a[q[i]][c[i]], a[p[i]][c[i]], 0));
    }
    
    auto ans = dijkstra(g, 0);

    cout << ans[N-1] << endl;
  }
  
  return 0;
}


Measured memory_bytes: 86448