#define _CRT_SECURE_NO_WARNINGS
#include "bits/stdc++.h"
#include <iostream>
#include <random>
#include <unordered_map>
#include <unordered_set>
#include <immintrin.h>
#ifdef _MSC_VER
#include <ppl.h>
#endif

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(i,a,n) for(int i=(a);i<(n);++i)
#define REP(i,n)  FOR(i,0,n)
#define all(j) (j).begin(), (j).end()
#define SZ(j) ((int)(j).size())
#define fake false



#define int long long
#define XY(x, y) (((x) << 32) | (y))

signed main() {

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

    int N, M;
    cin >> N >> M;

    unordered_map<ll, vector<pll>> G;
    REP(i, M) {
        int p, q, c;
        cin >> p >> q >> c;
        if (p > q) swap(p, q);

        if (p == 1) G[0].emplace_back(1, XY(c, p));
        G[XY(c, p)].emplace_back(0, XY(c, q));
        G[XY(c, p)].emplace_back(0, XY(0, p));
        G[XY(0, p)].emplace_back(1, XY(c, p));
        G[XY(c, q)].emplace_back(0, XY(c, p));
        G[XY(c, q)].emplace_back(0, XY(0, q));
        G[XY(0, q)].emplace_back(1, XY(c, q));
    }

    int V = G.size();
    const int INF = INT_MAX / 4;
    unordered_map<ll, int> d;
    for (auto& e : G) d[e.first] = INF;
    
    priority_queue<pll, vector<pll>, greater<pll>> pq;
    pq.emplace(0, 0);
    d[0] = 0;
    while (!pq.empty()) {
        int mincost, u;
        tie(mincost, u) = pq.top(); pq.pop();

        if (d[u] < mincost) continue;

        for (const auto& e : G[u]) {
            int v = e.second;
            if (d[u] + e.first < d[v]) {
                d[v] = d[u] + e.first;
                pq.emplace(d[v], v);
            }
        }
    }

    if (d.find(XY(0, N)) == d.end() || d[XY(0, N)] == INF) {
        cout << -1 << endl;
        return 0;
    }
    cout << d[XY(0, N)] << endl;

    return 0;
}


Measured memory_bytes: 82804