#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <map>
#include <memory>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
#include <random>
#include <tuple>
#include <iomanip>
#include <cstring>

using namespace std;

typedef long long ll;
//typedef pair<int,int> Pint;
//typedef pair<ll, ll> P;
//typedef pair<ll, pair<ll, ll>> P;
//typedef tuple<int,int,int> T;
typedef vector<ll> vec;
typedef vector<vec> mat;
#define rep(i, n) for(ll i = 0; i < (n); i++)
#define revrep(i, n) for(ll i = (n-1); i >= 0; i--)
#define pb push_back
#define f first
#define s second
//const ll INFL = 1LL << 60;//10^18 = 2^60
const ll INFL = 1LL << 60;
const int INF = 1 << 30;//10^9
ll MOD = 1000000007;
//ll MOD  = 998244353;
vector<ll> dy = {0, 0, 1, -1, 1, 1, -1, -1, 0};
vector<ll> dx = {1, -1, 0, 0, 1, -1, 1, -1, 0};

ll max(ll a, ll b){return (a > b) ? a : b;}
ll min(ll a, ll b){return (a < b) ? a : b;}
ll pow_long(ll x, ll k){
  ll res = 1;
  while(k > 0){
    if(k % 2) res *= x;
    x *= x;
    k /= 2;
  }
  return res;
}
ll pow_mod(ll x, ll k){
  x %= MOD; x += MOD; x %= MOD;
  ll res = 1;
  while(k > 0){
    if(k % 2){
      res *= x; res %= MOD;
    }
    x *= x; x %= MOD;
    k /= 2;
  }
  return res;
}
ll inverse(ll x){return pow_mod(x, MOD - 2);};

//最大公約数
ll gcd(ll a, ll b){
    if(b == 0) return a;
    return gcd(b, a % b);
}

//最小公倍数
ll lcm(ll x, ll y){return x / gcd(x, y) * y;};

ll kai_mod(ll x){
  if(x == 0) return 1;
  return x * kai_mod(x-1) % MOD;
}

//コンビネーション
const int MAXcomb = 200010;
ll fac[MAXcomb], finv[MAXcomb], inv[MAXcomb];
//facはn!,finvは1/n!
//invは逆元
void COMinit(){
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for(int i = 2; i < MAXcomb; i++){
        fac[i] = fac[i-1] * i % MOD;
        inv[i] = MOD - inv[MOD%i] * (MOD/i) % MOD;
        finv[i] = finv[i-1] * inv[i] % MOD;
    }
}
ll comb(int n, int k){
    if(n < k) return 0;
    if(n < 0 || k < 0) return 0;
    return fac[n] * finv[k] % MOD * finv[n-k] % MOD;
}

ll N, M;
map<pair<ll, ll>, ll> dist;
//頂点、会社
struct edge{ll to, com, cost;};
map<pair<ll, ll>, vector<edge>> E;

ll dijkstra(){
  dist[{0, -1}] = 1;
  //頂点、会社
  typedef pair<ll, pair<ll, ll>> P;
  priority_queue<P, vector<P>, greater<P>> pque;
  pque.push({1, {0, -1}});
  while(!pque.empty()){
    P p = pque.top();
    if(p.s.f == N-1){
      return p.f - 1;
    }
    pque.pop();
    if(dist[p.s] < p.f) continue;
    vector<edge> X = E[{p.s.f, p.s.s}];
    if(dist[{p.s.f, -1}] == 0 || dist[{p.s.f, -1}] > p.f){
      dist[{p.s.f, -1}] = p.f;
      pque.push({dist[{p.s.f, -1}], {p.s.f, -1}});
    }
    for(edge e : X){
      if(dist[{e.to, e.com}] == 0 || dist[{e.to, e.com}] > p.f + e.cost){
        dist[{e.to, e.com}] = p.f + e.cost;
        pque.push({dist[{e.to, e.com}], {e.to, e.com}});
      }
    }
  }
  return -1;
}

int main(){
  cin >> N >> M;
  rep(i, M){
    ll p, q, c;
    cin >> p >> q >> c;
    p--, q--;
    edge e = {p, c};
    E[{p, c}].pb({q, c, 0});
    E[{p, -1}].pb({q, c, 1});
    E[{q, c}].pb({p, c, 0});
    E[{q, -1}].pb({q, c, 1});
  }
  cout << dijkstra() << endl;
}


Measured memory_bytes: 95152