#include <iostream>
#include <string>
#include <cmath>
#include<algorithm>
#include<stack>
#include<queue>
#include<map>
#include<set>
#include<iomanip>
#define _USE_MATH_DEFINES
#include <math.h>
#include <functional>
#include<complex>
using namespace std;

#define rep(i,x) for(ll i=0;i<x;i++)
#define repn(i,x) for(ll i=1;i<=x;i++)

typedef long long ll;
const ll INF = 1e17;
const ll MOD = 998244353;
const ll MAX = 4000001;
const double eps = 1E-18;

ll max(ll a, ll b) {
	if (a > b) { return a; }
	return b;
}

ll min(ll a, ll b) {
	if (a > b) { return b; }
	return a;
}

ll gcd(ll a, ll b) {
	if (b == 0) { return a; }
	if (a < b) { return gcd(b, a); }
	return gcd(b, a % b);
}

ll lcm(ll a, ll b) {
	return a / gcd(a, b) * b;
}

struct edge {
	ll ind;
	ll fr;
	ll to;
	ll d;
};

class mint {
	long long x;
public:
	mint(long long x = 0) : x((x% MOD + MOD) % MOD) {}
	mint operator-() const {
		return mint(-x);
	}
	mint& operator+=(const mint& a) {
		if ((x += a.x) >= MOD) x -= MOD;
		return *this;
	}
	mint& operator-=(const mint& a) {
		if ((x += MOD - a.x) >= MOD) x -= MOD;
		return *this;
	}
	mint& operator*=(const  mint& a) {
		(x *= a.x) %= MOD;
		return *this;
	}
	mint operator+(const mint& a) const {
		mint res(*this);
		return res += a;
	}
	mint operator-(const mint& a) const {
		mint res(*this);
		return res -= a;
	}
	mint operator*(const mint& a) const {
		mint res(*this);
		return res *= a;
	}

	mint operator^(const ll& t)const {
		if (!t) return 1;
		mint a = pow(t >> 1);
		a *= a;
		if (t & 1) a *= *this;
		return a;
	}

	mint pow(ll t) const {
		if (!t) return 1;
		mint a = pow(t >> 1);
		a *= a;
		if (t & 1) a *= *this;
		return a;
	}
	// for prime MOD
	mint inv() const {
		return pow(MOD - 2);
	}
	mint& operator/=(const mint& a) {
		return (*this) *= a.inv();
	}
	mint operator/(const mint& a) const {
		mint res(*this);
		return res /= a;
	}

	friend ostream& operator<<(ostream& os, const mint& m) {
		os << m.x;
		return os;
	}
};

///////////////////////////

struct dijkstra {

	ll N;
	vector<vector<edge>> g;
	ll s;

	vector<ll> ans;

	dijkstra(ll N0, ll s, vector<vector<edge>> g0) {//頂点数、始点、グラフ(頂点は1indexか0index)
		N = N0;
		g = g0;

		ans.assign(N + 1, INF);


		priority_queue<pair<ll, ll>> q;//(-キョリ、頂点)

		ans[s] = 0;
		q.push({ 0,s });

		while (!q.empty()) {
			auto x = q.top();
			q.pop();

			ll dis = -x.first;
			ll v = x.second;

			if (dis > ans[v]) { continue; }


			for (edge e : g[v]) {
				ll w = e.to;
				if (dis + e.d < ans[w]) {
					ans[w] = dis + e.d;
					q.push({ -ans[w], w });
				}
			}


		}
	}

	ll d(ll t) {//sからtまでの最短距離を出力
		return ans[t];
	}


};


void dfs(ll v, map<ll,vector<ll>> &g, map<ll,ll> &cn,ll x) {
	//cout << v << x << endl;
	cn[v] = x;
	for (ll w : g[v]) {
		if (cn[w] != -1) { continue; }
		dfs(w, g, cn, x);
	}
}



int main() {
	ll N, M;
	cin >> N >> M;

	map<ll,map<ll, vector<ll>>> g;
	map<ll,map<ll, ll>> cn;

	set<ll> st;

	repn(i, M) {
		ll p, q, c;
		cin >> p >> q >> c;
		g[c][p].push_back(q);
		g[c][q].push_back(p);
		cn[c][p] = -1;
		cn[c][q] = -1;
		st.insert(c);
	}


	ll X = 0;
	for(ll c:st) {
		for (auto p : cn[c]) {
			ll v = p.first;
			if (p.second != -1) { continue; }
			X++;
			dfs(v, g[c], cn[c], X);
		}
	}

	vector<vector<edge>> h(N + X + 1);
	for(ll c:st) {
		for (auto p : cn[c]) {
			ll v = p.first;
			h[v].push_back({ 0,v,N + p.second,1 });
			h[N + p.second].push_back({ 0,N + p.second,v,1 });
		}
	}

	dijkstra dij(N+X, 1, h);

	ll ans = dij.ans[N];

	if (ans == INF) { ans = -1; }
	else { ans /= 2; }

	cout << ans << endl;

	system("PAUSE");
}


Measured memory_bytes: 231160