#define _CRT_SECURE_NO_WARNINGS
#include "bits/stdc++.h"
#include <random>
#include <unordered_map>
#include <unordered_set>
//#include <opencv2/core.hpp>
//#include <opencv2/highgui.hpp>
//#include <opencv2/imgproc.hpp>

using namespace std;

//呪文
#define DUMPOUT cerr
#define dump(...) DUMPOUT<<"  ";DUMPOUT<<#__VA_ARGS__<<" :["<<__LINE__<<":"<<__FUNCTION__<<"]"<<endl;DUMPOUT<<"    ";dump_func(__VA_ARGS__)

typedef unsigned uint; typedef long long ll; typedef unsigned long long ull; typedef pair<int, int> pii; typedef pair<ll, ll> pll; typedef pair<double, double> pdd; typedef pair<string, string> pss;
template <typename _KTy, typename _Ty> ostream& operator << (ostream& o, const pair<_KTy, _Ty>& m) { o << "{" << m.first << ", " << m.second << "}"; return o; }
template <typename _KTy, typename _Ty> ostream& operator << (ostream& o, const map<_KTy, _Ty>& m) { if (m.empty()) { o << "{ }"; return o; } o << "{" << *m.begin(); for (auto itr = ++m.begin(); itr != m.end(); itr++) { o << ", " << *itr; } o << "}"; return o; }
template <typename _KTy, typename _Ty> ostream& operator << (ostream& o, const unordered_map<_KTy, _Ty>& m) { if (m.empty()) { o << "{ }"; return o; } o << "{" << *m.begin(); for (auto itr = ++m.begin(); itr != m.end(); itr++) { o << ", " << *itr; } o << "}"; return o; }
template <typename _Ty> ostream& operator << (ostream& o, const vector<_Ty>& v) { if (v.empty()) { o << "{ }"; return o; } o << "{" << v.front(); for (auto itr = ++v.begin(); itr != v.end(); itr++) { o << ", " << *itr; } o << "}"; return o; }
template <typename _Ty> ostream& operator << (ostream& o, const set<_Ty>& s) { if (s.empty()) { o << "{ }"; return o; } o << "{" << *(s.begin()); for (auto itr = ++s.begin(); itr != s.end(); itr++) { o << ", " << *itr; } o << "}"; return o; }
template <typename _Ty> ostream& operator << (ostream& o, const unordered_set<_Ty>& s) { if (s.empty()) { o << "{ }"; return o; } o << "{" << *(s.begin()); for (auto itr = ++s.begin(); itr != s.end(); itr++) { o << ", " << *itr; }	o << "}"; return o; }
template <typename _Ty> ostream& operator << (ostream& o, const stack<_Ty>& s) { if (s.empty()) { o << "{ }"; return o; } stack<_Ty> t(s); o << "{" << t.top(); t.pop(); while (!t.empty()) { o << ", " << t.top(); t.pop(); } o << "}";	return o; }
template <typename _Ty> ostream& operator << (ostream& o, const list<_Ty>& l) { if (l.empty()) { o << "{ }"; return o; } o << "{" << l.front(); for (auto itr = ++l.begin(); itr != l.end(); ++itr) { o << ", " << *itr; } o << "}"; return o; }
template <typename _KTy, typename _Ty> istream& operator >> (istream& is, pair<_KTy, _Ty>& m) { is >> m.first >> m.second; return is; }
template <typename _Ty> istream& operator >> (istream& is, vector<_Ty>& v) { for (size_t i = 0; i < v.size(); i++) is >> v[i]; return is; }
namespace aux { // print tuple
	template<typename Ty, unsigned N, unsigned L> struct tp { static void print(ostream& os, const Ty& v) { os << get<N>(v) << ", "; tp<Ty, N + 1, L>::print(os, v); } };
	template<typename Ty, unsigned N> struct tp<Ty, N, N> { static void print(ostream& os, const Ty& v) { os << get<N>(v); } };
}
template<typename... Tys> ostream& operator<<(ostream& os, const tuple<Tys...>& t) { os << "{"; aux::tp<tuple<Tys...>, 0, sizeof...(Tys)-1>::print(os, t); os << "}"; return os; }

template<typename A, size_t N, typename T> inline void Fill(A(&array)[N], const T &val) { std::fill((T*)array, (T*)(array + N), val); }

void dump_func() { DUMPOUT << endl; }
template <class Head, class... Tail> void dump_func(Head&& head, Tail&&... tail) { DUMPOUT << head; if (sizeof...(Tail) == 0) { DUMPOUT << " "; } else { DUMPOUT << ", "; } dump_func(std::move(tail)...); }

#define PI 3.14159265358979323846
#define EPS 1e-10
#define FOR(is,a,n) for(int is=(a);is<(n);++is)
#define REP(is,n)  FOR(is,0,n)
#define all(j) (j).begin(), (j).end()
#define SZ(j) ((int)(j).size())
#define fake false



const int INF = 1 << 29;

template<typename T>
class edge {
public:
	T from, to, cost;

	edge() : from(0), to(T(0)), cost(T(0)) {}
	edge(T from, T to) : from(from), to(to), cost(T(1)) {}
	edge(T from, T to, T cost) : from(from), to(to), cost(cost) {}
};

template<typename T>
class Dijkstra {

	// d[i] : 始点 s から頂点 i への最短距離
	// d[i] = min(d[j] + (j から i への辺のコスト) | e = (j, i) in E)
	vector<T> d;
	vector<T> prev;

public:

	typedef pair<T, T> pTT;

	// Dijkstra 法 O(|E|log|V|) (負の辺がない場合)
	// G : 隣接リスト, V : 頂点数, s : スタート地点
	// edge の from は使わないので -1 とか入れとく
	Dijkstra(const vector<vector<edge<T>>>& G, T V, T s)
		: d(V, INF), prev(V, -1)
	{
		// pll(最短距離, 頂点の番号)
		priority_queue<pTT, vector<pTT>, greater<pTT>> pq;

		d[s] = 0;
		pq.push(pTT(0, s));

		while (!pq.empty()) {
			pTT p = pq.top(); pq.pop();
			// まだ使われていない頂点のうち距離が最小のもの
			T v = p.second;
			if (d[v] < p.first) continue;
			for (T i = 0; i < G[v].size(); i++) {
				edge<T> e = G[v][i];
				if (d[e.to] > d[v] + e.cost) {
					d[e.to] = d[v] + e.cost;
					prev[e.to] = v;
					pq.push(pTT(d[e.to], e.to));
				}
			}
		}
	}

	vector<T> shortest_path_cost() { return d; }
	T shortest_path_cost(T v) { return d[v]; }

	vector<T> get_path(T t) {
		vector<T> path;
		// t が s になるまで prev[t] を辿っていく
		for (; t != -1; t = prev[t]) path.push_back(t);
		reverse(path.begin(), path.end());
		return path;
	}

};

int main() {

	cin.tie(0);
	ios::sync_with_stdio(false);

	int N, M;
	cin >> N >> M;
	
	vector<edge<int>> es;
	unordered_map<ll, int> cmp;
	for (ll i = 0; i < N; i++)
		cmp[(i << 32) - 1] = i;
	for (int i = 0; i < M; i++) {
		ll p, q, c;
		cin >> p >> q >> c;
		p--; q--;
		ll v = (p << 32) + c;
		ll w = (q << 32) + c;
		if (cmp.find(v) == cmp.end()) {
			int sz = cmp.size();
			cmp[v] = sz;
		}
		if (cmp.find(w) == cmp.end()) {
			int sz = cmp.size();
			cmp[w] = sz;
		}
		es.push_back(edge<int>(p, cmp[v], 1));
		es.push_back(edge<int>(cmp[v], p, 0));
		es.push_back(edge<int>(q, cmp[w], 1));
		es.push_back(edge<int>(cmp[w], q, 0));
		es.push_back(edge<int>(cmp[v], cmp[w], 0));
		es.push_back(edge<int>(cmp[w], cmp[v], 0));
	}

	vector<vector<edge<int>>> G(cmp.size());
	for (const auto e : es)
		G[e.from].push_back(edge<int>(-1, e.to, e.cost));

	int cost = Dijkstra<int>(G, G.size(), 0).shortest_path_cost(N - 1);
	cout << (cost == INF ? -1 : cost) << endl;

	return 0;
}


Measured memory_bytes: 74080