//四則演算 #pragma GCC target("avx")
//並列計算 #pragma GCC optimize("O3")
//条件分岐を減らす #pragma GCC optimize("unroll-loops")
//浮動小数点演算 #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using VI = vector<int>;
using VL = vector<ll>;
using VS = vector<string>;
template<class T> using PQ = priority_queue<T, vector<T>, greater<T>>;
#define FOR(i,a,n) for(int i=(a);i<(n);++i)
#define eFOR(i,a,n) for(int i=(a);i<=(n);++i)
#define rFOR(i,a,n) for(int i=(n)-1;i>=(a);--i)
#define erFOR(i,a,n) for(int i=(n);i>=(a);--i)
#define each(i, a) for(auto &i : a)
#define SORT(a) sort(a.begin(),a.end())
#define rSORT(a) sort(a.rbegin(),a.rend())
#define fSORT(a,f) sort(a.begin(),a.end(),f)
#define all(a) a.begin(),a.end()
#define out(y,x) ((y)<0||h<=(y)||(x)<0||w<=(x))
#define tp(a,i) get<i>(a)
#define line cout << "-----------------------------\n" 
#define ENDL(i,n) ((i) == (n) - 1 ? "\n" : " ")
#define stop system("pause")
constexpr ll INF = 1000000000;
constexpr ll LLINF = 1LL << 60;
constexpr ll mod = 1000000007;
constexpr ll MOD = 998244353;
constexpr ld eps = 1e-10;
constexpr ld pi = 3.1415926535897932;
template<class T>inline bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; }return false; }
template<class T>inline bool chmin(T& a, const T& b) { if (a > b) { a = b; return true; }return false; }
inline void init() { cin.tie(nullptr); cout.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(15); }
template<class T>inline istream& operator>>(istream& is, vector<T>& v) { for (auto& a : v)is >> a; return is; }
template<class T>inline istream& operator>>(istream& is, deque<T>& v) { for (auto& a : v)is >> a; return is; }
template<class T, class U>inline istream& operator>>(istream& is, pair<T, U>& p) { is >> p.first >> p.second; return is; }
template<class T>inline vector<T> vec(size_t a) { return vector<T>(a); }
template<class T>inline vector<T> defvec(T def, size_t a) { return vector<T>(a, def); }
template<class T, class... Ts>inline auto vec(size_t a, Ts... ts) { return vector<decltype(vec<T>(ts...))>(a, vec<T>(ts...)); }
template<class T, class... Ts>inline auto defvec(T def, size_t a, Ts... ts) { return vector<decltype(defvec<T>(def, ts...))>(a, defvec<T>(def, ts...)); }
template<class T>inline void print(const T& a) { cout << a << "\n"; }
template<class T, class... Ts>inline void print(const T& a, const Ts&... ts) { cout << a << " "; print(ts...); }
template<class T>inline void print(const vector<T>& v) { for (int i = 0; i < v.size(); ++i)cout << v[i] << (i == v.size() - 1 ? "\n" : " "); }
template<class T>inline void print(const vector<vector<T>>& v) { for (auto& a : v)print(a); }
inline string reversed(const string& s) { string t = s; reverse(all(t)); return t; }

int main() {
    init();

    int n, m; cin >> n >> m;
    vector<vector<vector<tuple<int, int, int>>>> g(n);
    vector<map<int, int>> ma(n);
    FOR(i, 0, m) {
        int a, b, c; cin >> a >> b >> c;
        --a, --b;

        int s, t;
        if (ma[a].count(c))s = ma[a][c];
        else {
            ma[a][c] = s = g[a].size();
            g[a].emplace_back(vector<tuple<int, int, int>>());
        }
        if (ma[b].count(c))t = ma[b][c];
        else {
            ma[b][c] = t = g[b].size();
            g[b].emplace_back(vector<tuple<int, int, int>>());
        }
        g[a][s].emplace_back(b, t, 0);
        g[b][t].emplace_back(a, s, 0);
    }

    if (g[0].empty()) {
        print(-1);
        return 0;
    }

    vector<VI> dp(n);
    FOR(i, 0, n) {
        if (g[i].empty())continue;
        g[i].emplace_back(vector<tuple<int, int, int>>());
        FOR(j, 0, g[i].size() - 1) {
            g[i][j].emplace_back(i, g[i].size() - 1, 0);
            g[i][g[i].size() - 1].emplace_back(i, j, 1);
        }
        dp[i].resize(g[i].size(), INF);
    }
    dp[0][g[0].size() - 1] = 0;
    deque<pair<int, int>> bfs;
    bfs.emplace_back(0, g[0].size() - 1);

    while (!bfs.empty()) {
        int cur, idx;
        tie(cur, idx) = bfs.front();
        bfs.pop_front();
        each(dest, g[cur][idx]) {
            int to, next_idx, cost;
            tie(to, next_idx, cost) = dest;
            if (!chmin(dp[to][next_idx], dp[cur][idx] + cost))continue;
            if (cost == 0)bfs.emplace_front(to, next_idx);
            else bfs.emplace_back(to, next_idx);
        }
    }

    print(dp[n - 1].empty() || dp[n - 1].back() == INF ? -1 : dp[n - 1].back());

    return 0;
}

Measured memory_bytes: 70400