#include <vector>
#include <iostream>
#include <cmath>
#include <map>
#include <unordered_map>
#include <algorithm>
#include <fstream>
#include <unistd.h>
#include <string.h>
#include <string>
#include <numeric>
#include <queue>
#include <deque>
#include <sstream>
#include <iomanip>
#include <set>
#include <stack>
#include <cassert>
#include <functional>
#include <random>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<vvl> vvvl;
typedef vector<vvvl> vvvvl;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef vector<bool> vb;
typedef vector<vector<bool>> vvb;
typedef vector<vvb> vvvb;
typedef vector<vvvb> vvvvb;
typedef vector<string> vs;
typedef vector<vs> vvs;
typedef vector<vvs> vvvs;
typedef vector<char> vc;
typedef vector<vector<char>> vvc;
typedef vector<double> vd;
typedef vector<vd> vvd;
typedef vector<vvd> vvvd;
typedef pair<ll, ll> PL;
typedef vector<PL> vpl;
typedef vector<vector<PL>> vvpl;
typedef vector<vvpl> vvvpl;
typedef pair<ll, PL> TL;
typedef vector<TL> vtl;
typedef vector<vtl> vvtl;
const int INF = 1001001001;
const ll LINF = 1e17;
const double pi = 3.1415926535897932;
const string endstr = "\n";
#define FOR(i, a, b) for(ll i = (a); i < b; i++)
#define RFOR(i, a, b) for(ll i = (a); i > b; i--)
#define rep(i, n) for(ll i = 0; i < n; i++)
#define rrep(i, n) for(ll i = n-1; i > -1; i--)
#define FORMAP(it, m) for(auto it = m.begin(); it != m.end(); it++)
#define ff first
#define ss second
#define pb push_back
#define epb emplace_back
#define ALL(X) (X).begin(),(X).end()

template <typename T>
T gcd(T a, T b) {
    return (a == 0) ? b : gcd(b%a, a);
}
template <typename T>
T lcm(T a, T b) {
    return a / gcd(a, b) * b;
}

bool p_comp_fs(const PL p1, const PL p2){ return p1.first < p2.first;};
bool p_comp_fg(const PL p1, const PL p2){ return p1.first > p2.first;};
bool p_comp_ss(const PL p1, const PL p2){ return p1.second < p2.second;};
bool p_comp_sg(const PL p1, const PL p2){ return p1.second > p2.second;};
template <typename T>
vector<T> uniquen(vector<T> vec){
    sort(ALL(vec));
    vec.erase(unique(vec.begin(), vec.end()), vec.end());
    return vec;
}

inline ll popcnt(ll x){return __builtin_popcountll((unsigned long long)x);};
template<class T> bool chmax(T &a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> bool chmin(T &a, T b) { if (a > b) { a = b; return true; } return false; }
//friend bool operator<(const stc& lhs, const stc& rhs){
//    return std::tie(lhs.l, lhs.r) < std::tie(rhs.l, rhs.r);
//}


int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    ll N, M; cin >> N >> M;
    vl P(M), Q(M), C(M);
    rep(i, M){
        ll p, q, c; cin >> p >> q >> c; p--; q--;
        P[i] = p; Q[i] = q; C[i] = c;
    }
    vector<PL> compress;
    rep(i, N) compress.pb({i, -1});
    rep(i, M){
        compress.pb({P[i], C[i]});
        compress.pb({Q[i], C[i]});
    }
    sort(ALL(compress));
    compress = uniquen(compress);
    
    map<PL, ll> idxes;
    ll idx = 0;
    for(auto p : compress){
        idxes[p] = idx; idx++;
    }
    
    vvpl G(compress.size());
    for(auto p : compress){
        if(p.second == -1) continue;
        ll station = p.first;
        ll outidx = idxes[{station, -1}];
        ll curidx = idxes[p];
        G[curidx].push_back({outidx, 0});
        G[outidx].push_back({curidx, 1});
    }
    rep(i, M){
        ll sidx = idxes[{P[i], C[i]}], tidx = idxes[{Q[i], C[i]}];
        G[sidx].push_back({tidx, 0});
        G[tidx].push_back({sidx, 0});
    }
    
    // 01-bfs
    deque<ll> dq;
    vl dist(compress.size(), LINF);
    PL st = {0,-1}; dist[idxes[st]] = 0;
    dq.pb(idxes[st]);
    while (!dq.empty()) {
        ll now = dq.front(); dq.pop_front();
        for(auto p : G[now]){
            ll cost = p.second;
            ll to = p.first;
            if(dist[to] > dist[now] + cost){
                dist[to] = dist[now] + cost;
                if(cost == 0) dq.push_front(to);
                else dq.push_back(to);
            }
        }
    }
    ll ans = dist[idxes[{N-1, -1}]];
    cout << (ans == LINF ? -1 : ans) << endstr;;
    return 0;
}


Measured memory_bytes: 92896