#pragma GCC optimize("Ofast")

#include <bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
#include <random>

using namespace std;
using namespace __gnu_pbds;

typedef long long ll;

typedef
tree<ll, null_type, less<ll>, rb_tree_tag, tree_order_statistics_node_update> orderedSet;

#define pb push_back
#define F first
#define S second
#define all(a) (a).begin(), (a).end()

#define for1(i0, l0, r0) for (int i0 = l0; i0 < r0; ++i0)
#define for2(i0, l0, r0) for (int i0 = l0; i0 <= r0; ++i0)
#define forn(i0, n0) for (int i0 = 0; i0 < n0; ++i0)
#define forn1(i0, n0) for (int i0 = 1; i0 < n0; ++i0)
#define forr(i0, n0) for (int i0 = n0; i0 >= 0; --i0)
#define forr1(i0, r0, l0) for (int i0 = r0; i0 > l0; --i0)
#define forr2(i0, r0, l0) for (int i0 = r0; i0 >= l0; --i0)

#define Sort(a) sort(all(a))
#define Reverse(a) reverse(all(a))
#define relaxMax(a, b) a = max(a, b)
#define relaxMin(a, b) a = min(a, b)

typedef long double ld;
#define ui unsigned int
#define ull unsigned long long

typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<double, double> pdd;
typedef pair<string, string> pss;

typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<double> vd;
typedef vector<ld> vld;
typedef vector<bool> vb;
typedef vector<string> vs;

typedef vector<pii> vpii;
typedef vector<pll> vpll;
typedef vector<pdd> vpdd;

typedef vector<vi> vvi;
typedef vector<vd> vvd;
typedef vector<vll> vvll;
typedef vector<vb> vvb;

#define vpss vector<pss>
#define vvs vector<vs>
#define vvpii vector<vpii>
#define vvpll vector<vpll>
#define vpt vector<pt>
#define vvvi vector<vvi>
#define vsi vector<set<int>>
#define ss second
#define ff first

#define printvi(arr) for (int x0 : arr) cout << x0 << ' '; cout << '\n';
#define printvll(arr) for (ll x0 : arr) cout << x0 << ' '; cout << '\n';
#define printpair(pair0) cout << pair0.F << ' ' << pair0.S << '\n';
#define printvp(arr) for (auto pair0 : arr) printpair(pair0);
#define initArray(arr, N0, X0) memset(arr, X0, N0 * sizeof(int))
//mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

void init() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    //cout.precision(16);
    //freopen("input.txt", "r", stdin);
    //freopen("output.txt", "w", stdout);
}

const int maxn = 1e6 + 5;

vvi companies(maxn);
vvi E(maxn, vi(3));
vvi components;

void findComponents(int company) {
    set<int> V;
    map<int, vi> g;
    for (int ei: companies[company]) {
        int v = E[ei][0], u = E[ei][1];
        V.insert(v);
        V.insert(u);
        g[v].pb(u);
        g[u].pb(v);
    }
    while (!V.empty()) {
        vi component;
        int v0 = *V.begin();
        V.erase(v0);
        component.pb(v0);
        queue<int> q;
        q.push(v0);
        while (!q.empty()) {
            int v = q.front();
            q.pop();
            for (int u : g[v]) {
                if (V.count(u)) {
                    V.erase(u);
                    q.push(u);
                    component.pb(u);
                }
            }
        }
        components.pb(component);
    }
}

void solve() {
    int n, m;
    cin >> n >> m;
    forn(i, m) {
        forn(j, 3) cin >> E[i][j];
        E[i][0]--, E[i][1]--;
        companies[E[i][2]].pb(i);
    }
    forn(i, maxn) {
        findComponents(i);
    }
    vvi in(n);
    forn(i, components.size()) {
        for (int j : components[i]) in[j].pb(i);
    }
    vi d(n, -1);
    d[0] = 0;
    queue<int> q;
    q.push(0);
    vb used(maxn);
    while (!q.empty()) {
        int v = q.front();
        q.pop();
        for (int c : in[v]){
            if (used[c]) continue;
            used[c] = 1;
            for (int u : components[c]){
                if (d[u] == -1){
                    d[u] = d[v] + 1;
                    q.push(u);
                }
            }
        }
    }
    cout << d[n - 1] << '\n';
}

bool multitest = false;

int main() {
    init();
    int t = 1;
    if (multitest) cin >> t;
    forn(i, t) solve();
}

Measured memory_bytes: 105084