#include <bits/stdc++.h>
 
// #include <iostream> // cout, endl, cin
// #include <string> // string, to_string, stoi
// #include <vector> // vector
// #include <algorithm> // min, max, swap, sort, reverse, lower_bound, upper_bound
// #include <utility> // pair, make_pair
// #include <tuple> // tuple, make_tuple
// #include <cstdint> // int64_t, int*_t
// #include <cstdio> // printf
// #include <map> // map
// #include <queue> // queue, priority_queue
// #include <set> // set
// #include <stack> // stack
// #include <deque> // deque
// #include <unordered_map> // unordered_map
// #include <unordered_set> // unordered_set
// #include <bitset> // bitset
// #include <climits>
// #include <cmath>
// #include <iomanip>
// #include <functional>
// #include <numeric>
// #include <random>
 
using namespace std;
    
#define int long long
#define pb push_back
#define F first
#define S second
#define FOR(i,a,b) for(int (i)=(a);(i)<(b);(i)++)
#define rep(i,n) FOR(i,0,n)
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()
#define ve vector
#define vi vector<int>
#define vp vector<pair<int,int>>
#define vvi vector<vector<int>>
 
template<typename T> using pq = priority_queue<T,vector<T>,greater<T>>; 
using ll = long long;
ll INF = LLONG_MAX / 4000 - 100;
ll mod = 1e9 + 7;
int dx[] = {-1,0,1,0}, dy[] = {0,1,0,-1};
vector<ll> prime;

double pi = 3.141592653689793238;
    
class fact {
public:
    int fmod = 1e9+7;
    vector<int> fac, finv, inv;
    fact (int n, int Mod = 1e9+7) {
        fmod = Mod;
        fac = vector<int>(n + 1, 0);
        finv = vector<int>(n + 1, 0);
        inv = vector<int>(n + 1, 0);
        fac[0] = 1; for (int i = 1; i < n + 1; i++) fac[i] = fac[i-1] * i % fmod;
        for (int i = 0;i < n + 1;i++) finv[i] = fact::POW(fac[i], fmod-2);
        for (int i = 0;i < n + 1;i++) inv[i] = POW(i, fmod-2);
    }
    ll nCr(ll n, ll r) {if(n < r) return 0; return (fac[n] * finv[r] % fmod) * finv[n-r] % fmod;}
    ll POW(ll a, ll b) {ll c = 1; while (b > 0) {if (b & 1) {c = a * c%fmod;}a = a * a%fmod; b >>= 1;}return c;}
    inline int operator [] (int i) {return fac[i];}
};
    
void DEBUG(vector<int> a) {for(int i=0;i<a.size();i++)cout<<a[i]<<" ";cout<<endl;}
void EMP(int x) {cout<<"!!!"<<x<<"!!!"<<endl;}
ll GCD(ll a, ll b) {ll c; while (b != 0) {c = a % b; a = b; b = c;}return a;}
ll LCM(ll a, ll b) {return (a / GCD(a, b)) * (b / GCD(a, b)) * GCD(a, b);}
ll POW(ll a, ll b) {ll c = 1; while (b > 0) {if (b & 1) {c = a * c%mod;}a = a * a%mod; b >>= 1;}return c;}
void PRI(ll n) {bool a[n + 1LL]; for (int i = 0; i < n + 1LL; i++) {a[i] = 1LL;}for (int i = 2; i < n + 1LL; i++) {if (a[i]) {prime.pb(i); ll b = i; while (b <= n) {a[b] = 0; b += i;}}}}
template <typename T> T chmin(T& a, T b) {if(a>b)a=b;return a;}
template <typename T> T chmax(T& a, T b) {if(a<b)a=b;return b;}
bool isSqrt(ll a) {return pow(sqrt(a),2) == a ? 1 : 0;}
void YesNo(bool a) {if (a) cout << "Yes"; else cout << "No"; cout << endl;}
void yesno(bool a) {if (a) cout << "yes"; else cout << "no"; cout << endl;}
void YESNO(bool a) {if (a) cout << "YES"; else cout << "NO"; cout << endl;}
double dis(int x1, int x2, int y1, int y2) {
    return sqrt((double)abs(x1-x2)*(double)abs(x1-x2)+(double)abs(y1-y2)*(double)abs(y1-y2));
}
int ceili(int x, int y) {
    if (x % y == 0) return x / y;
    else return x / y + 1;
}
 
long long extGCD(long long a, long long b, long long &x, long long &y) {
    if (b == 0) {
        x = 1;
        y = 0;
        return a;
    }
    long long d = extGCD(b, a % b, y, x);
    y -= a / b * x;
    return d;
}


class UnionFind {
private:
    vector<int> par;
public:
    UnionFind(){}
    UnionFind(int N) { par = vector<int>(N, -1); }
    int find(int x);
    ll size(int x);
    void unite(int x, int y);
    bool same(int x, int y);
};
 
int UnionFind::find(int x) {
    if (par[x] < 0) return x;
    else return par[x] = find(par[x]);
}
 
ll UnionFind::size(int x) {
    return -par[find(x)];
}
 
void UnionFind::unite(int x, int y) {
    x = find(x);
    y = find(y);
    if (x == y) return;
    //大きい方に小さい方をくっ付ける
    if (size(x) < size(y)) swap(x, y);
    par[x] += par[y];
    par[y] = x;
}
 
bool UnionFind::same(int x, int y) {
    x = find(x);
    y = find(y);
    return x == y;
}

map<int, vector<pair<int, int>>> g;
const int sk = 1e6+5;

void solve() {
    int n, m; cin >> n >> m;
    map<int, int> cost;
    vector<set<int>> to(n);
    rep (i, m) {
        int p, q, c; cin >> p >> q >> c; --p, --q;
        g[p * sk + c].pb({q * sk + c, c});
        g[q * sk + c].pb({p * sk + c, c});
        to[p].insert(c), to[q].insert(c);
    }
    rep (i, n) {
        cost[sk * i] = INF;
    }
    for (auto elm : g) cost[elm.first] = INF;
    pq<pair<int, int>> q;
    cost[0] = 0;
    q.push({0, 0});
    while (q.size()) {
        int now = q.top().second, cst = q.top().first; q.pop();
        // cout << now / sk << " " << now % sk << " " << cst << endl;
        if (cost[now] != cst) continue;
        if (now % sk == 0) {
            //改札
            for (auto elm : to[now / sk]) {
                if (cost[now + elm] > cst + 1) {
                    cost[now + elm] = cst + 1;
                    q.push({cost[now + elm], now + elm});
                }
            }
        } else {
            for (auto elm : g[now]) {
                if (cost[elm.first] > cst) {
                    cost[elm.first] = cst;
                    q.push({cost[elm.first], elm.first});
                }
                if (cost[now - now % sk] > cst) {
                    cost[now - now % sk] = cst;
                    q.push({cost[now - now % sk], now - now % sk});
                }
            }
        }
    }

    cout << ((cost[(n - 1) * sk] == INF) ? -1 : cost[(n - 1) * sk]) << endl;
    return;
}
 
signed main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    solve();
}

Measured memory_bytes: 103536