#include <iostream>
#include <sstream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <ctime>
#include <cstring>
#include <string>
#include <vector>
#include <stack>
#include <queue>
#include <deque>
#include <map>
#include <set>
#include <bitset>
#include <numeric>
#include <utility>
#include <iomanip>
#include <algorithm>
#include <functional>
#include <unordered_map>
using namespace std;

#define COUT(x) cout << #x << " = " << (x) << " (L" << __LINE__ << ")" << endl
#define EACH(i, s) for (__typeof__((s).begin()) i = (s).begin(); i != (s).end(); ++i)

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
template<class T1, class T2> ostream& operator << (ostream &s, pair<T1,T2> P)
{ return s << '<' << P.first << ", " << P.second << '>'; }
template<class T> ostream& operator << (ostream &s, vector<T> P)
{ for (int i = 0; i < P.size(); ++i) { if (i > 0) { s << " "; } s << P[i]; } return s; }
template<class T> ostream& operator << (ostream &s, vector<vector<T> > P)
{ for (int i = 0; i < P.size(); ++i) { s << endl << P[i]; } return s << endl; }
template<class T1, class T2> ostream& operator << (ostream &s, map<T1,T2> P)
{ EACH(it, P) { s << "<" << it->first << "->" << it->second << "> "; } return s << endl; }


typedef pair<int,int> pint;
map<pint,int> ma;
set<int> used;
int E;


vector<pint> G[110000];
vector<int> nG[510000];
int n, m;


int INF = 1<<29;
int dp[510000];

int solve() {
    deque<pint> deq;
    for (int i = 0; i < 510000; ++i) dp[i] = INF;
    deq.push_back( pint(E,0) );
    dp[E] = 0;
    
    while (!deq.empty()) {
        int v = deq.front().first;
        int dist = deq.front().second;
        deq.pop_front();

        if ( dp[v] < dist ) continue;
        
        //cout << v << ", " << c << ": " << dp[ ma[ pint(v,c) ]] << endl;
        
        for (int i = 0; i < nG[v].size(); ++i) {
            int nv = nG[v][i];
            
            if (v < E && nv < E) {
                if (chmin(dp[nv], dp[v])) {
                    deq.push_front(pint(nv, dp[nv]));
                }
            }
            else {
                if (chmin(dp[nv], dp[v] + 1)) {
                    deq.push_back(pint(nv, dp[nv]));
                }
            }
        }
    }
    
    int res = dp[E + n-1];
    if (res >= INF) return -1;
    else return res/2;
}


int main() {
    while (cin >> n >> m) {
        for (int i = 0; i < m; ++i) {
            int p, q, c;
            scanf("%d %d %d", &p, &q, &c);
            --p, --q, --c;
            G[p].push_back(pint(q, c));
            G[q].push_back(pint(p, c));
            ma[pint(p,c)] = 0;
            ma[pint(q,c)] = 0;
        }
        int con = 0;
        for (map<pint,int>::iterator it = ma.begin(); it != ma.end(); ++it) {
            it->second = con++;
        }
        E = (int)ma.size();
        
        for (int i = 0; i < n; ++i) {
            for (int j = 0; j < G[i].size(); ++j) {
                int to = G[i][j].first;
                int c = G[i][j].second;
                
                int u = ma[pint(i,c)];
                int v = ma[pint(to,c)];
                
                nG[u].push_back(v);
                nG[v].push_back(u);
                
                if (!used.count(u)) {
                    nG[u].push_back(E + i);
                    nG[E + i].push_back(u);
                    used.insert(u);
                }
            }
        }
        
        cout << solve() << endl;
    }
}


















Measured memory_bytes: 83200