#pragma GCC optimize("Ofast")
#include<bits/stdc++.h>
// #include<ext/pb_ds/assoc_container.hpp>
// #include<ext/pb_ds/tree_policy.hpp>
// #include<ext/pb_ds/tag_and_trait.hpp>
// using namespace __gnu_pbds;
// #include<boost/multiprecision/cpp_int.hpp>
// namespace multiprecisioninteger = boost::multiprecision;
// using cint=multiprecisioninteger::cpp_int;
using namespace std;
using ll=long long;
#define double long double
using datas=pair<ll,ll>;
using ddatas=pair<double,double>;
using tdata=pair<ll,datas>;
using vec=vector<ll>;
using mat=vector<vec>;
using pvec=vector<datas>;
using pmat=vector<pvec>;
// using llset=tree<ll,null_type,less<ll>,rb_tree_tag,tree_order_statistics_node_update>;
#define For(i,a,b) for(i=a;i<(ll)b;++i)
#define bFor(i,b,a) for(i=b,--i;i>=(ll)a;--i)
#define rep(i,N) For(i,0,N)
#define rep1(i,N) For(i,1,N)
#define brep(i,N) bFor(i,N,0)
#define brep1(i,N) bFor(i,N,1)
#define all(v) (v).begin(),(v).end()
#define allr(v) (v).rbegin(),(v).rend()
#define vsort(v) sort(all(v))
#define vrsort(v) sort(allr(v))
#define endl "\n"
#define eb emplace_back
#define print(v) cout<<v<<endl
#define printyes cout<<"Yes"<<endl
#define printno cout<<"No"<<endl
#define printYES cout<<"YES"<<endl
#define printNO cout<<"NO"<<endl
#define output(v) do{bool f=0;for(auto outi:v){cout<<(f?" ":"")<<outi;f=1;}cout<<endl;}while(0)
const ll mod=1000000007;
// const ll mod=998244353;
const ll inf=1LL<<60;
const double PI = acos(-1);
const double eps = 1e-9;
template<class T> inline bool chmax(T& a,T b){bool x=a<b;if(x)a=b;return x;} 
template<class T> inline bool chmin(T& a,T b){bool x=a>b;if(x)a=b;return x;} 

void startupcpp(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout<<fixed<<setprecision(15);
}

double distance(ddatas x,ddatas y){
  double a=x.first-y.first,b=x.second-y.second;
  return sqrt(a*a+b*b);
}

ll modinv(ll a) {
  ll b=mod,u=1,v=0,t;
  while(b){
    t=a/b;
    a-=t*b; swap(a,b);
    u-=t*v; swap(u,v);
  }
  return (u+mod)%mod;
}

ll moddevide(ll a,ll b){return (a*modinv(b))%mod;}

vec modncrlistp,modncrlistm;

ll modncr(ll n,ll r){
  if(n<r)return 0;
  ll i,size=modncrlistp.size();
  if(size<=n){
    modncrlistp.resize(n+1);
    modncrlistm.resize(n+1);
    if(!size){
      modncrlistp[0]=modncrlistm[0]=1;
      size++;
    }
    For(i,size,n+1){
      modncrlistp[i]=modncrlistp[i-1]*i%mod;
      modncrlistm[i]=modinv(modncrlistp[i]);
    }
  }
  return modncrlistp[n]*modncrlistm[r]%mod*modncrlistm[n-r]%mod;
}

ll modpow(ll a,ll n){
  ll res=1;
  while(n>0){
    if(n&1)res=res*a%mod;
    a=a*a%mod;
    n>>=1;
  }
  return res;
}

ll gcd(ll a,ll b){if(!b)return a;return (a%b==0)?b:gcd(b,a%b);}
ll lcm(ll a,ll b){return a/gcd(a,b)*b;}

ll countdigits(ll n){
  ll ans=0;
  while(n){n/=10;ans++;}
  return ans;
}

ll sumdigits(ll n){
  ll ans=0;
  while(n){ans+=n%10;n/=10;}
  return ans;
}
int main(){
  // startupcpp();
  // int codeforces;cin>>codeforces;while(codeforces--){
  ll i,N,M,cnt=0,ans=inf;
  cin>>N>>M;
  vec a(M),b(M),c(M),finlis,chst;
  mat eqst(N);
  map<datas,ll> mp;
  rep(i,M){
    cin>>a[i]>>b[i]>>c[i];
    --a[i];--b[i];--c[i];
    if(!mp[datas(a[i],c[i])]){
      eqst[a[i]].eb(cnt);
      chst.eb(a[i]);
      if(a[i]==N-1)finlis.eb(cnt);
      mp[datas(a[i],c[i])]=++cnt;
    }
    if(!mp[datas(b[i],c[i])]){
      eqst[b[i]].eb(cnt);
      chst.eb(b[i]);
      if(b[i]==N-1)finlis.eb(cnt);
      mp[datas(b[i],c[i])]=++cnt;
    }
  }
  mat g(cnt);
  vec dist(cnt,inf);
  deque<datas> que;
  rep(i,M){
    g[mp[datas(a[i],c[i])]-1].eb(mp[datas(b[i],c[i])]-1);
    g[mp[datas(b[i],c[i])]-1].eb(mp[datas(a[i],c[i])]-1);
    if(!a[i]||!b[i]){
      que.eb(1,mp[datas(a[i],c[i])]-1);
    }
  }
  eqst[0].clear();
  while(!que.empty()){
    datas x=que.front();que.pop_front();
    if(!chmin(dist[x.second],x.first))continue;
    for(ll next:g[x.second]){
      if(dist[next]==inf)que.emplace_front(x.first,next);
    }
    if(eqst[chst[x.second]].size()){
      for(ll next:eqst[chst[x.second]]){
        que.eb(x.first+1,next);
      }
      eqst[chst[x.second]].clear();
    }
  }
  for(ll x:finlis)chmin(ans,dist[x]);
  if(ans==inf)ans=-1;
  print(ans);
  return 0;
}

Measured memory_bytes: 69100