#define _CRT_SECURE_NO_WARNINGS
#define _SCL_SECURE_NO_WARNINGS
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <iostream>
#include <string>
#include <vector>
#include <list>
#include <utility>
#include <algorithm>
#include <functional>
#include <cmath>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <iomanip>
#include <sstream>
#include <bitset>
#include <limits>
#include <numeric>
#include <valarray>
#include <fstream>

using namespace std;
typedef unsigned int uint;
typedef long long LL;
typedef unsigned long long ULL;
typedef pair<LL, LL> PP;
#define REP(i,a,n) for(LL i = (a); i < (LL)(n); ++i)
#define REM(i,a,n) for(LL i = ((n) - 1); i >= (a); --i)
#define FLOAT fixed << setprecision(16)
#define SPEEDUP {cin.tie(NULL); ios::sync_with_stdio(false);}
const int INF = 0x3FFFFFFF;
const LL INFLL = 0x3FFFFFFF3FFFFFFF;
const double INFD = 1.0e+308;
const string INFSTR = "\x7f";
const double EPS = 1.0e-9;

void YesNo(bool b) { cout << (b ? "Yes" : "No") << endl; }
void YESNO(bool b) { cout << (b ? "YES" : "NO") << endl; }
template <class T, class U>
istream& operator>>(istream& ist, pair<T, U>& right) { return ist >> right.first >> right.second; }
template <class T, class U>
ostream& operator<<(ostream& ost, const pair<T, U>& right) { return ost << right.first << ' ' << right.second; }
template <class T, class TCompatible, size_t N>
void Fill(T(&dest)[N], const TCompatible& val) { fill(dest, dest + N, val); }
template <class T, class TCompatible, size_t M, size_t N>
void Fill(T(&dest)[M][N], const TCompatible& val) { for (int i = 0; i < M; ++i) Fill(dest[i], val); }
template<class T>
T Compare(T left, T right) { return left > right ? 1 : (left < right ? -1 : 0); }
istream& Ignore(istream& ist) { string s; ist >> s; return ist; }
bool Inside(int i, int j, int h, int w) { return i >= 0 && i < h && j >= 0 && j < w; }
// all_of
// partial_sum, adjacent_difference

#ifdef ONLY_MY_ENVIR
#include "IntMod.h"
#include "Union_Find.h"
#include "Graph.h"
#include "Range.h"
#include "Global.h"
#include "Flow_Solver.h"
#include "Tree.h"
#include "Suffix_Array.h"
#include "Geometry.h"
#include "Matrix.h"
#endif

#ifdef __GNUC__
typedef __int128 LLL;
istream& operator>> (istream& ist, __int128& val) { LL tmp;  ist >> tmp; val = tmp; return ist; }
ostream& operator<< (ostream& ost, __int128 val) { LL tmp = val; ost << tmp; return ost; }
#endif

#if 1234567891
#include <array>
#include <random>
#include <unordered_set>
#include <unordered_map>
template<typename T>
using PriorityQ = priority_queue<T, vector<T>, greater<T> >;	// コスト小を優先
#endif

using TT = pair<PP, int>;

int N, M;
vector<PP> G[100000];
int dist[100000];
map<int,vector<int>> avail[100000];
set<TT> used;

int main() {
	cin >> N >> M;
	REP(i, 0, M) {
		int a, b, c;
		cin >> a >> b >> c;
		--a; --b;
		G[a].push_back(PP(b, c));
		G[b].push_back(PP(a, c));
		avail[a][c].push_back(b);
		avail[b][c].push_back(a);
	}

	int times = 0;
	set<int> prev, now;
	prev.insert(0);
	Fill(dist, INF);

	while (!prev.empty()) {
		now.clear();

		vector<PP> look;
		for (int from : prev) {
			if (times < dist[from]) dist[from] = times;
		}

		for (int from : prev) {
			for (auto&& e : G[from]) {
				int to = e.first;
				int line = e.second;
				TT t = TT(PP(min(from, to), max(from, to)), line);
				if (used.count(t) > 0) continue;
				used.insert(t);

				stack<int> st;
				st.push(to);
				while (!st.empty()) {
					int from = st.top(); st.pop();
					now.insert(from);
					for (int to : avail[from][line]) {
						TT t = TT(PP(min(from, to), max(from, to)), line);
						if (used.count(t) > 0) continue;
						 used.insert(t);

						st.push(to);
					}
				}
			}
		}

		prev = move(now);
		++times;
	}
	cout << (dist[N - 1] == INF ? -1 : dist[N - 1]) << endl;
	return 0;
}


Measured memory_bytes: 78720