#include <bits/stdc++.h>
using namespace std;
/*{{{*/  //template
#define rep(i,n) for(int i=0;i<n;i++)
constexpr int INF = numeric_limits<int>::max()/2;
constexpr long long LINF = numeric_limits<long long>::max()/3;
#define mp make_pair
#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define all(v) (v).begin(),(v).end()
#define sz(x) (int)(x).size()
#define debug(x) cerr<<#x<<":"<<x<<endl
#define debug2(x,y) cerr<<#x<<","<<#y":"<<x<<","<<y<<endl
//struct fin{ fin(){ cin.tie(0); ios::sync_with_stdio(false); } } fin_;
struct Double{ double d; explicit Double(double x) : d(x){} };
ostream& operator<<(ostream& os,const Double x){ os << fixed << setprecision(20) << x.d; return os; }
template<typename T> ostream& operator<<(ostream& os,const vector<T>& vec){ os << "["; for(const auto& v : vec){ os << v << ","; } os << "]"; return os; }
template<typename T,typename U> ostream& operator<<(ostream& os,const pair<T,U>& p){ os << "(" << p.first << ","<< p.second <<")"; return os; }
template<typename T> ostream& operator<<(ostream& os,const set<T>& st){ os<<"{"; for(T v:st) os<<v<<","; os <<"}"; return os; }
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
ll gcd(ll a,ll b){ if(b==0) return a; else return gcd(b,a%b); }
//constexpr double eps = 1e-14; 
constexpr double eps = 1e-10; 
constexpr ll mod = 1e9+7;
const int dx[]={1,0,-1,0} ,dy[] = {0,1,0,-1};
/*}}}*/

int N,M;
int P[200200],Q[200200],C[200200];

using Vertex = pair<int,int>;   // {node,color}
using State = pair<int,Vertex>; // {dist,vertex}

map<Vertex,vector<pair<int,Vertex>>> graph;
set<int> colst;
set<int> rcol[200200];

int main(){
    cin >> N >> M;
    rep(i,M){
        cin >> P[i] >> Q[i] >> C[i];
        P[i]--;
        Q[i]--;
        graph[Vertex(P[i],C[i])].eb(mp(0,Vertex(Q[i],C[i])));
        graph[Vertex(Q[i],C[i])].eb(mp(0,Vertex(P[i],C[i])));
        rcol[P[i]].insert(C[i]);
        rcol[Q[i]].insert(C[i]);
    }

    for(int i=0;i<N;i++){
        for(int c : rcol[i]){
            graph[Vertex(i,0)].eb(mp(1,Vertex(i,c)));
            graph[Vertex(i,c)].eb(mp(0,Vertex(i,0)));
        }
    }

    //cerr << "show graph" << endl;
    //for(auto& v : graph){
    //    cerr << v.first << " " << v.second << endl;
    //}

    map<Vertex,int> d;

    for(auto x : graph){
        Vertex v = x.fi;
        d[v] = INF;
        for(auto y : x.se){
            d[y.se] = INF;
        }
    }

    Vertex s(0,0),t(N-1,0);
    d[s] = 0;

    priority_queue<State,vector<State>,greater<State>> que;
    que.push(State(0,s));
    while(!que.empty()){
        State state = que.top();que.pop();
        Vertex vertex = state.se;
        int dist = state.fi;
        int node = vertex.fi;
        int col = vertex.se;
        if(d[vertex] < dist) continue;

        for(auto edge : graph[vertex]){
            int cost = edge.fi;
            int nnode = edge.se.fi;
            int ncol = edge.se.se;
            if(d[Vertex(nnode,ncol)] > cost + dist){
                State nxt(dist + cost , Vertex(nnode,ncol));
                d[Vertex(nnode,ncol)] = cost + dist;
                que.push(nxt);
            }
        }
    }

    if(d[t]==0 or d[t]==INF) cout << -1 << endl;
    else cout << d[t] << endl;
}


Measured memory_bytes: 125104