#include<bits/stdc++.h>
using namespace std;
 
#define ALL(a)  (a).begin(),(a).end()
#define ALLR(a)  (a).rbegin(),(a).rend()
#define spa << " " <<
#define lfs <<fixed<<setprecision(10)<<
#define test cout<<"test"<<endl;
#define fi first
#define se second
#define MP make_pair
#define PB push_back
#define EB emplace_back
#define rep(i,n,m) for(ll i = n; i < (ll)(m); i++)
#define rrep(i,n,m) for(ll i = n - 1; i >= (ll)(m); i--)
typedef int ll;
typedef long double ld;
const ll MOD = 1e9+7;
//const ll MOD = 998244353;
const ll INF = 1e9;
using P = pair<ll, ll>;
template<typename T>
void chmin(T &a,T b){if(a>b)a=b;}
template<typename T>
void chmax(T &a,T b){if(a<b)a=b;}
void pmod(ll &a,ll b){a=(a+b)%MOD;}
void pmod(ll &a,ll b,ll c){a=(b+c)%MOD;}
void qmod(ll &a,ll b){a=(a*b)%MOD;}
void qmod(ll &a,ll b,ll c){a=(b*c)%MOD;}
ll median(ll a,ll b, ll c){return a+b+c-max({a,b,c})-min({a,b,c});}
void ans1(bool x){if(x) cout<<"Yes"<<endl;else cout<<"No"<<endl;}
void ans2(bool x){if(x) cout<<"YES"<<endl;else cout<<"NO"<<endl;}
void ans3(bool x){if(x) cout<<"Yay!"<<endl;else cout<<":("<<endl;}
template<typename T1,typename T2>
void ans(bool x,T1 y,T2 z){if(x)cout<<y<<endl;else cout<<z<<endl;}  
template<typename T>
void debug(vector<vector<T>>v,ll h,ll w){for(ll i=0;i<h;i++)
{cout<<v[i][0];for(ll j=1;j<w;j++)cout spa v[i][j];cout<<endl;}};
void debug(vector<string>v,ll h,ll w){for(ll i=0;i<h;i++)
{for(ll j=0;j<w;j++)cout<<v[i][j];cout<<endl;}};
template<typename T>
void debug(vector<T>v,ll n){cout<<v[0];
for(ll i=1;i<n;i++)cout spa v[i];cout<<endl;};
template<typename T>
vector<vector<T>>vec(ll x, ll y, T w){
  vector<vector<T>>v(x,vector<T>(y,w));return v;}
ll gcd(ll x,ll y){ll r;while(y!=0&&(r=x%y)!=0){x=y;y=r;}return y==0?x:y;}
template<typename T>
void emp(map<T,ll>&m, T x){m.emplace(x,0).first->second++;}
vector<ll>dx={1,0,-1,0,1,1,-1,-1};
vector<ll>dy={0,1,0,-1,1,-1,1,-1};
 
struct edge{
  ll t,c;
};
struct z{
  ll v,p;//vertex,price,company
};
int main(){
  cin.tie(NULL);
  ios_base::sync_with_stdio(false);
  ll res=0,res1=INF,res2=-INF,buf=0;
  bool judge = true;
  ll n,m;cin>>n>>m;
  vector<vector<edge>>g(n);
  rep(i,0,m){
    ll p,q,c;
    cin>>p>>q>>c;
    g[p-1].push_back({q-1,c});
    g[q-1].push_back({p-1,c});
  }
  deque<struct z>deq;
  deq.PB({0,0});
  vector<ll>d(n,INF);
  vector<unordered_set<ll>>st(n);
  d[0]=0;
  while(!deq.empty()){
    struct z x=deq.front();
    deq.pop_front();
    rep(i,0,g[x.v].size()){
      ll k=x.p+(st[x.v].find(g[x.v][i].c)==st[x.v].end());
      //cout<<x.v spa k<<endl;
      if(k==d[g[x.v][i].t]){
        if(st[g[x.v][i].t].find(g[x.v][i].c)
          ==st[g[x.v][i].t].end()){
          st[g[x.v][i].t].insert(g[x.v][i].c);
          if(k==x.p){
          deq.push_front({g[x.v][i].t,k});
          }
        }
      }
      else if(k<d[g[x.v][i].t]){
        d[g[x.v][i].t]=k;
        unordered_set<ll>tmp;
        tmp.insert(g[x.v][i].c);
        st[g[x.v][i].t]=tmp;
        if(k==x.p){
          deq.push_front({g[x.v][i].t,k});
        }
        else deq.push_back({g[x.v][i].t,k});
      }
    }
    //cout<<x.v spa x.p spa st[x.v].size()<<endl; 
    //debug(d,n);
    /*rep(j,0,n){
      cout<<j+1<<endl;
      for(auto z:st[j])cout<<z<<" ";
      cout<<endl;
    }*/
  }
  ans(d[n-1]==INF,-1,d[n-1]);
  return 0;
}

Measured memory_bytes: 24960