#include <bits/stdc++.h>  // clang-format off
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define each(x,v) for(auto& x : v)
#define all(v) (v).begin(),(v).end()
#define sz(v) ((int)(v).size())
#define ini(...) int __VA_ARGS__; in(__VA_ARGS__)
#define inl(...) long long __VA_ARGS__; in(__VA_ARGS__)
#define ins(...) string __VA_ARGS__; in(__VA_ARGS__)

#ifdef ONLINE_JUDGE
  #define rep(i,N) for(int i = 0; i < (int)(N); i++)
  #define repr(i,N) for(int i = (int)(N) - 1; i >= 0; i--)
  #define rep1(i,N) for(int i = 1; i <= (int)(N) ; i++)
  #define repr1(i,N) for(int i = (N) ; (int)(i) > 0 ; i--)
#else
  #define rep(i,N) for(long long i = 0; i < (long long)(N); i++)
  #define repr(i,N) for(long long i = (long long)(N) - 1; i >= 0; i--)
  #define rep1(i,N) for(long long i = 1; i <= (long long)(N) ; i++)
  #define repr1(i,N) for(long long i = (N) ; (long long)(i) > 0 ; i--)
#endif

using namespace std; void solve();
using ll = long long; template<class T = ll> using V = vector<T>;
using vi = V<int>; using vl = V<>; using vvi = V< V<int> >;
constexpr int inf = 1001001001; constexpr ll infLL = (1LL << 61) - 1;
struct IoSetupNya {IoSetupNya() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(15); cerr << fixed << setprecision(7);} } iosetupnya;
template<typename T, typename U> inline bool amin(T &x, U y) { return (y < x) ? (x = y, true) : false; }
template<typename T, typename U> inline bool amax(T &x, U y) { return (x < y) ? (x = y, true) : false; }
template<typename T, typename U> ostream& operator <<(ostream& os, const pair<T, U> &p) { os << p.first << " " << p.second; return os; }
template<typename T, typename U> istream& operator >>(istream& is, pair<T, U> &p) { is >> p.first >> p.second; return is; }
template<typename T> ostream& operator <<(ostream& os, const vector<T> &v) { int s = (int)v.size(); for(int i=0;i<s;i++) os << (i ? " " : "") << v[i]; return os; }
template<typename T> istream& operator >>(istream& is, vector<T> &v) { for(auto &x : v) is >> x; return is; }
void in(){} template <typename T,class... U> void in(T &t,U &...u){ cin >> t; in(u...);}
void out(){cout << "\n";} template <typename T,class... U> void out(const T &t,const U &...u){ cout << t; if(sizeof...(u)) cout << " "; out(u...);}
template<typename T>void die(T x){out(x); exit(0);}

#ifdef NyaanDebug
  #include "NyaanDebug.h"
  #define trc(...) do { cerr << #__VA_ARGS__ << " = "; dbg_out(__VA_ARGS__);} while(0)
  #define trca(v,N) do { cerr << #v << " = "; array_out(v , N);} while(0)
  #define trcc(v) do { cerr << "name : " << #v << "\n"; int cnt = 0; each(x , v){cerr << (cnt++) << " : "; trc(x); } } while(0)
#else
  #define trc(...)
  #define trca(...)
  #define trcc(...)
  int main(){solve();}
#endif

#define inc(...) char __VA_ARGS__; in(__VA_ARGS__)
#define in2(s,t)   rep(i,sz(s)){in(s[i] , t[i]);}
#define in3(s,t,u) rep(i,sz(s)){in(s[i] , t[i] , u[i]);}
using vd = V<double>; using vs = V<string>; using vvl = V< V<> >;
template<typename T,typename U>ll ceil(T a,U b){return (a + b - 1) / b;}

using P = pair<int,int>; using vp = V<P>;
constexpr int MOD = /**/ 1000000007; //*/ 998244353;
// clang-format on
///////////////////////////////////////////////////////////


template< typename T >
struct edge {
  int src, to;
  T cost;

  edge(int to, T cost) : src(-1), to(to), cost(cost) {}
  edge(int src, int to, T cost) : src(src), to(to), cost(cost) {}

  edge &operator=(const int &x) {
    to = x;
    return *this;
  }

  operator int() const { return to; }
};
template< typename T >
using Edges = vector< edge< T > >;
template< typename T >
using WeightedGraph = vector< Edges< T > >;
using UnweightedGraph = vector< vector <int> >;

// グラフの入力
UnweightedGraph graph(
  int N , int M = -1 , bool is_directed = false, bool is_1origin = true){
  UnweightedGraph g(N);
  if(M == -1) M = N - 1;
  for(int _ = 0 ; _ < M ; _++){
    int x , y; cin >> x >> y;
    if(is_1origin) x-- , y--;
    g[x].pb(y);
    if(!is_directed) g[y].pb(x);
  }
  return g;
}

// 重み付きグラフの入力
template<typename T>
WeightedGraph<T> wgraph(
  int N , int M = -1 , bool is_directed = false , bool is_1origin = true){
  WeightedGraph<T> g(N);
  if(M == -1) M = N - 1;
  for(int _ = 0 ; _ < M ; _++){
    int x , y; cin >> x >> y;
    T c; cin >> c;
    if(is_1origin) x-- , y--;
    g[x].eb(y , c);
    if(!is_directed) g[y].eb(x , c);
  }
  return g;
}


// dijkstra 到達不可能な場合はINFを返す
template<typename T>
vector<T> dijkstra(WeightedGraph<T> &g, int start = 0){ 
  using P = pair<T , int>;
  int N = (int)g.size();
  T INF = numeric_limits<T>::max() / 2;
  vector<T> d(N , INF);
  priority_queue<P , vector<P> , greater<P> > Q;
  d[start] = 0;
  Q.emplace(0 , start);
  while(!Q.empty()){
    P p = Q.top(); Q.pop();
    int cur = p.second;
    if(d[cur] < p.first) continue;
    for(auto dst : g[cur]){
      if( d[cur] + dst.cost < d[dst]){
        d[dst] = d[cur] + dst.cost;
        Q.emplace(d[dst] , dst);
      }
    }
  }
  return d;
}

void solve(){
  ini(N , M);
  WeightedGraph<int> g(N + 2 * M);
  map<P , int> m;
  int idx = N;
  auto add = [&](int p,int c) -> void{
    if(m.find(P(p , c)) == m.end()){
      m[P(p , c)] = idx;
      g[p].emplace_back(idx , 1);
      g[idx].emplace_back(p , 0);
      idx++;
    }
  };

  rep(i , M){
    ini(p , q , c); p--,q--;
    add(p , c);
    add(q , c);
    int s = m[P(p , c)];
    int t = m[P(q , c)];
    g[s].eb(t , 0);
    g[t].eb(s , 0);
  }
  trcc(m);
  trc(g);
  
  g.resize(idx);
  auto d = dijkstra(g);
  trc(d);
  out(d[N - 1] > inf ? -1 : d[N - 1]);


}


Measured memory_bytes: 61044