#include "bits/stdc++.h"
#include "ext/pb_ds/assoc_container.hpp"
#include "ext/pb_ds/tree_policy.hpp"
using namespace __gnu_pbds;
using namespace std;
typedef long long ll;
#define int long long
#define pb push_back
#define fi first
#define se second
#define fr(i, a, b) for(int i = a; i <= b; i++)
#define all(x) x.begin(), x.end()
#define IO ios :: sync_with_stdio(0), cin.tie(0), cout.tie(0)
#define pii pair<int,int>
#define sz(x) (int)x.size()
const int mod = 1e9 + 7;
// const int mod1 = 998244353;
typedef long double f80;
 
#ifndef LOCAL
#pragma GCC optimize ("O2")
#define endl '\n'
#endif
 
template<typename T>
using ordered_set = tree<T,null_type,less<T>,rb_tree_tag,tree_order_statistics_node_update>;
 
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
int rand(int l, int r){
    uniform_int_distribution<int> uid(l, r);
    return uid(rng);
}
 
ll pwr(ll a,ll b, ll mod){
    a %= mod;
    int ans = 1;
    while(b){
        if(b & 1) ans = (ans * a) % mod;
        a = (a * a) % mod;
        b >>= 1;
    }
    return ans;
}
 
string to_string(string s) {
  return '"' + s + '"';
}
 
string to_string(const char* s) {
  return to_string((string) s);
}
 
string to_string(bool b) {
  return (b ? "true" : "false");
}
 
template <typename A, typename B>
string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
 
template <typename A>
string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}
 
void debug_out() { cerr << endl; }
 
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}
 
#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif

void debug1(int a[], int l,int r) {
	#ifdef LOCAL
		vector<int> temp(a + l, a + r + 1);
		debug(temp);
	#endif
}

const int N = 5e5 + 5;
map<pii,int> m;
int cc = 0;

vector<pii> g[N];
int dist[N];
void add(int p,int q) {
	if(!m.count({p, q})){
		m[{p, q}] = ++cc;
		dist[cc] = 1e18;
	}
	if(q > 0) {
		int u = m[{p, 0}], v = m[{p, q}];
		g[u].pb({v, 1});
		g[v].pb({u, 0});
	}
}

void solve(){
	int n, mm;
	cin >> n >> mm;
	fr(i, 1, n) {
		add(i, 0);
	}
	fr(i, 1, mm) {
		int p, q, r;
		cin >> p >> q >> r;
		add(p, r);
		add(q, r);
		int u = m[{p, r}], v = m[{q, r}];
		g[u].pb({v, 0});
		g[v].pb({u, 0});
	}
	multiset<pii> q;
	int s = m[{1, 0}], t = m[{n, 0}];
	q.insert({0, s});
	dist[s] = 0;
	while(!q.empty()) {
		pii u = (*q.begin());
		q.erase(q.begin());
		for(pii v : g[u.se]) {
			if(dist[v.fi] > dist[u.se] + v.se) {
				dist[v.fi] = dist[u.se] + v.se;
				q.insert({dist[v.fi], v.fi});
			}
		}
	}
	if(dist[t] == 1e18) {
		cout << -1;
		return;
	}
	cout << dist[t];
}

signed main(){
    IO;
    #ifdef LOCAL
        freopen("inp.txt","r", stdin);
        freopen("out.txt", "w", stdout);
    #endif
    cout << setprecision(10) << fixed;
    int t = 1;
    // cin >> t;
    fr(tt, 1, t){
        solve();
    }
    return 0;
} 

Measured memory_bytes: 87664