#include <bits/stdc++.h>
using namespace std;

#define llong long long 
#define len(x) ((int)x.size())
#define rep(i,n) for (int i = -1; ++ i < n; )
#define rep1(i,n) for (int i = 0; i ++ < n; )
#define rand __rand
mt19937 rng(chrono::system_clock::now().time_since_epoch().count());  // or mt19937_64
template<class T = int> T rand(T range = numeric_limits<T>::max()) { return (T)(rng() % range); }

#define CONCAT_(x, y) x##y/*{{{*/
#define CONCAT(x, y) CONCAT_(x, y)
#ifdef LOCAL_DEBUG   
int __db_level = 0;
bool __db_same_line = false;
#define clog cerr << string(!__db_same_line ? __db_level * 2 : 0, ' ')
struct debug_block {
    function<void()> fn;
    void print_name() { __db_same_line = true; fn(); clog << endl; __db_same_line = false;  }
    debug_block(function<void()> fn_): fn(fn_) { clog << "{ "; print_name(); ++__db_level; }
    ~debug_block() { --__db_level; clog << "} "; print_name(); }
};
#define DB(args...) debug_block CONCAT(dbbl, __LINE__)([=]{ clog << args; })
#define deb(...)  if (1) { (clog << "[" #__VA_ARGS__ "] = [" << __VA_ARGS__) << "]"; if (!__db_same_line) clog << endl; }
#else
#define clog if (0) cerr
#define DB(...)
#define deb(...)
#endif
template<class T>
ostream& operator,(ostream& out, const T& thing) { return out << ", " << thing; }
template<class U, class V>
ostream& operator<<(ostream& out, const pair<U, V>& p) { return (out << "(" << p.first, p.second) << ")"; }
template<class A, class B>
ostream& operator<<(ostream& out, const tuple<A, B>& t) { return (out << "(" << get<0>(t), get<1>(t)) << ")"; }
template<class A, class B, class C>
ostream& operator<<(ostream& out, const tuple<A, B, C>& t) { return (out << "(" << get<0>(t), get<1>(t), get<2>(t)) << ")"; }
template<class T> ostream& operator<<(ostream& out, const vector<T>& container) { 
    out << "{";
    if (len(container)) out << container[0];
    rep1(i, len(container) - 1) out, container[i];
    return out << "}";
}
template<class x> vector<typename x::value_type> $v(const x& a) { return vector<typename x::value_type>(a.begin(), a.end()); }
#define ptrtype(x) typename iterator_traits<x>::value_type
template<class u> vector<ptrtype(u)> $v(u a, u b) { return vector<ptrtype(u)>(a, b); }/*}}}*/
// ACTUAL SOLUTION BELOW ////////////////////////////////////////////////////////////

const int maxn = 101010;
int n, m;
int dist[maxn];
set<int> reached_from[maxn];
map<int, vector<int>> gr[maxn];

int main(void) {
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    cin >> n >> m;
    rep(i, m) {
        int u, v, c; cin >> u >> v >> c;
        gr[u][c].emplace_back(v);
        gr[v][c].emplace_back(u);
    }
    
    fill(dist, dist + n + 1, INT_MAX);
    dist[1] = 0;
    vector<int> cur(1, 1);
    
    while (len(cur)) {
        queue<pair<int, int>> qu;
        for (auto& u: cur) for (auto c: reached_from[u]) qu.emplace(u, c);
        for (; qu.size(); qu.pop()) {
            auto [u, c] = qu.front();
            for (auto v: gr[u][c]) {
                if (reached_from[v].count(c)) continue;
                reached_from[v].insert(c);
                if (dist[v] == INT_MAX) {
                    cur.push_back(v);
                    dist[v] = dist[u];
                }
                qu.emplace(v, c);
            }
        }
        
        vector<int> nxt;
        for (auto u: cur) {
            for (auto& [c, gv]: gr[u]) {
                if (reached_from[u].count(c)) continue;
                for (auto& v: gv) {
                    if (dist[v] == dist[u] + 1) {
                        reached_from[v].insert(c);
                    }
                    if (dist[v] != INT_MAX) continue;
                    dist[v] = dist[u] + 1;
                    reached_from[v].insert(c);
                    nxt.push_back(v);
                }
            }
        }
        cur = move(nxt);
    }
    
    if (dist[n] == INT_MAX) dist[n] = -1;
    cout << dist[n];

    return 0;
}

// Remember:
// - Multitest? REFRESHING the data!!!
// - Constrains for each set of data may differs. Should NOT USE the same max constant (maxn)
//   for all of them.
// vim: foldmethod=marker



Measured memory_bytes: 75992