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

using i64 = int64_t;

#define rep(i, x, y) for (i64 i = i64(x), i##_max_for_repmacro = i64(y); i < i##_max_for_repmacro; ++i)
#define debug(x) #x << "=" << (x)

#ifdef DEBUG
#define _GLIBCXX_DEBUG
#define print(x) std::cerr << debug(x) << " (L:" << __LINE__ << ")" << std::endl
#else
#define print(x)
#endif

template <i64 p>
class fp {
    public:
    i64 x;
    fp() : x(0) {}
    fp(i64 x_) : x((x_ % p + p) % p) {}
    fp operator+() const { return fp(x); }
    fp operator-() const { return fp(-x); }
    fp& operator+=(const fp& y) {
        x += y.x;
        if (x >= p) x -= p;
        return *this;
    }
    fp& operator-=(const fp& y) { return *this += -y; }
    fp& operator*=(const fp& y) {
        x = x * y.x % p;
        return *this;
    }
    fp& operator/=(const fp& y) { return *this *= fp(inverse(y.x)); }
    fp operator+(const fp& y) const { return fp(x) += y; }
    fp operator-(const fp& y) const { return fp(x) -= y; }
    fp operator*(const fp& y) const { return fp(x) *= y; }
    fp operator/(const fp& y) const { return fp(x) /= y; }
    bool operator==(const fp& y) const { return x == y.x; }
    bool operator!=(const fp& y) const { return !(*this == y); }
    i64 extgcd(i64 a, i64 b, i64& x, i64& y) {
        i64 d = a;
        if (b != 0) {
            d = extgcd(b, a % b, y, x);
            y -= (a / b) * x;
        } else {
            x = 1;
            y = 0;
        }
        return d;
    }
    i64 inverse(i64 a) {
        i64 x, y;
        extgcd(a, p, x, y);
        return (x % p + p) % p;
    }
};

template <i64 p>
i64 abs(const fp<p>& x) { return x.x; }

template <i64 p>
istream& operator>>(istream& is, fp<p>& x) {
    is >> x.x;
    return is;
}

template <i64 p>
ostream& operator<<(ostream& os, const fp<p>& x) {
    os << x.x;
    return os;
}

template <typename T, typename U>
ostream& operator<<(ostream& os, const pair<T, U>& p) {
    os << "(" << p.first << ", " << p.second << ")";
    return os;
}

template <typename T>
ostream& operator<<(ostream& os, const vector<T>& vec) {
    os << "[";
    for (const auto& v : vec) {
        os << v << ",";
    }
    os << "]";
    return os;
}

template <typename T>
bool chmin(T& a, const T& b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}

template <typename T>
bool chmax(T& a, const T& b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}

template <typename A, typename T, size_t size>
void fill(A (&ary)[size], const T& val) {
    fill((T*)ary, (T*)(ary + size), val);
}

// x未満の要素の個数を返す
template <typename T>
i64 count_less(const vector<T>& v, T x) {
    return lower_bound(begin(v), end(v), x) - begin(v);
}

// x以下の要素の個数を返す
template <typename T>
i64 count_less_or_equal(const vector<T>& v, T x) {
    return upper_bound(begin(v), end(v), x) - begin(v);
}

// xより大きい要素の個数を返す
template <typename T>
i64 count_greater(const vector<T>& v, T x) {
    return end(v) - upper_bound(begin(v), end(v), x);
}

// x以上の要素の個数を返す
template <typename T>
i64 count_greater_or_equal(const vector<T>& v, T x) {
    return end(v) - lower_bound(begin(v), end(v), x);
}

// x未満の要素のうち最大のものを返す
template <typename T>
T max_less(const vector<T>& v, T x) {
    return *(lower_bound(begin(v), end(v), x) - 1);
}

// x以下の要素のうち最大のものを返す
template <typename T>
T max_less_or_equal(const vector<T>& v, T x) {
    return *(upper_bound(begin(v), end(v), x) - 1);
}

// xより大きい要素のうち最小のものを返す
template <typename T>
T min_greater(const vector<T>& v, T x) {
    return *upper_bound(begin(v), end(v), x);
}

// x以上の要素のうち最小のものを返す
template <typename T>
T min_greater_or_equal(const vector<T>& v, T x) {
    return *lower_bound(begin(v), end(v), x);
}

constexpr int inf = 1.01e9;
constexpr i64 inf64 = 4.01e18;
constexpr long double eps = 1e-9;

// 実数値のn分探索のループ回数の上限(2分探索なら50でも十分かもしれない)
constexpr i64 max_loop = 100;

void solve() {
    //constexpr i64 mod = 1'000'000'007;
    i64 N,M;
    cin >> N >> M;

    vector<i64> p(M),q(M),c(M);
    rep(i,0,M){
        cin >> p[i] >> q[i] >> c[i];
        --p[i];
        --q[i];
        --c[i];
    }

    vector<vector<i64>> kind(N);
    rep(i,0,M){
        kind[p[i]].emplace_back(c[i]);
        kind[q[i]].emplace_back(c[i]);
    }

    constexpr i64 out=-1;
    rep(i,0,N) kind[i].emplace_back(out);

    vector<unordered_map<i64,i64>> to_idx(N);
    rep(i,0,N){
        rep(j,0,kind[i].size()){
            to_idx[i][kind[i][j]]=j;
        }
    }

    vector<vector<vector<i64>>> graph(N);
    rep(i,0,N){
        graph[i].resize(kind[i].size());
    }
    rep(i,0,M){
        graph[p[i]][to_idx[p[i]][c[i]]].emplace_back(q[i]);
        graph[q[i]][to_idx[q[i]][c[i]]].emplace_back(p[i]);
    }

    vector<vector<i64>> dist(N);
    rep(i,0,N){
        dist[i].resize(kind[i].size(),inf64);
    }
    using tup=tuple<i64,i64,i64>;
    priority_queue<tup,vector<tup>,greater<tup>> que;

    dist[0][to_idx[0][out]]=0;
    que.push(make_tuple(0,0,to_idx[0][out]));
    while(!que.empty()){
        i64 distance,station,company_idx;
        tie(distance, station, company_idx)=que.top();
        que.pop();

        i64 company=kind[station][company_idx];

        if(dist[station][company_idx] < distance) continue;

        const i64 out_idx=to_idx[station][out];

        if(company_idx != out_idx){
            // 駅の外に出る
            if(distance<dist[station][out_idx]){
                dist[station][out_idx]=distance;
                que.push(make_tuple(distance,station,out_idx));
            }

            // 路線を利用する
            for(i64 next_station:graph[station][company_idx]){
                const i64 next_company_idx=to_idx[next_station][company];
                if(distance<dist[next_station][next_company_idx]){
                    dist[next_station][next_company_idx]=distance;
                    que.push(make_tuple(distance,next_station,next_company_idx));
                }
            }
        }else{
            // 改札に入る
            const i64 next_distance=distance+1;
            rep(i,0,kind[station].size()){
                if(kind[station][i]==out) continue;

                if(next_distance<dist[station][i]){
                    dist[station][i]=next_distance;
                    que.push(make_tuple(next_distance,station,i));
                }
            }
        }
    }

    i64 ans=inf64;
    rep(i,0,kind[N-1].size()) chmin(ans,dist[N-1][i]);

    cout << (ans==inf64?-1:ans) << endl;
}

int main() {
    std::cin.tie(0);
    std::ios::sync_with_stdio(false);
    cout.setf(ios::fixed);
    cout.precision(16);
    solve();
    return 0;
}


Measured memory_bytes: 84204