#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC push_options
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx")
#include<bits/stdc++.h>
#include <xmmintrin.h>
#include <immintrin.h>
using namespace::std;
__attribute__((constructor))void init(){cin.tie(0);ios::sync_with_stdio(false);cout<<fixed<<setprecision(15);}
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/priority_queue.hpp>
#include<ext/pb_ds/tag_and_trait.hpp>
// #include <boost/multiprecision/cpp_dec_float.hpp>
// #include <boost/multiprecision/cpp_int.hpp>
// namespace mp = boost::multiprecision;
// typedef mp::number<mp::cpp_dec_float<0>> cdouble;
// typedef mp::cpp_int cint;
template<typename T>using pbds=__gnu_pbds::tree<T,__gnu_pbds::null_type,less<T>,__gnu_pbds::rb_tree_tag,__gnu_pbds::tree_order_statistics_node_update>;
template<typename T>using pbds_map=__gnu_pbds::tree<T,T,less<T>,__gnu_pbds::rb_tree_tag,__gnu_pbds::tree_order_statistics_node_update>;
template<typename T,typename E>using hash_map=__gnu_pbds::gp_hash_table<T,E>;
template<typename T>using pqueue =__gnu_pbds::priority_queue<T, greater<T>,__gnu_pbds::rc_binomial_heap_tag>;
typedef long long lint;
#define INF (1LL<<60)
#define IINF (1<<30)
#define LINF (9223372036854775807LL)
#define EPS (1e-10)
#define endl ('\n')
#define MOD 1000000007LL
//#define MOD 998244353LL
typedef vector<lint> vec;
typedef vector<vector<lint>> mat;
typedef vector<vector<vector<lint>>> mat3;
typedef vector<string> svec;
typedef vector<vector<string>> smat;
template<typename T>inline void numout(T t){bool f=0;for(auto i:t){cout<<(f?" ":"")<<i<INF/2?i:"INF";f=1;}cout<<endl;}
template<typename T>inline void numout2(T t){for(auto i:t)numout(i);}
template<typename T>inline void output(T t){bool f=0;for(auto i:t){cout<<(f?" ":"")<<i;f=1;}cout<<endl;}
template<typename T>inline void output2(T t){for(auto i:t)output(i);}
template<typename T>inline void _output(T t){bool f=0;for(lint i=0;i<t.size();i++){cout<<f?"":" "<<t[i];f=1;}cout<<endl;}
template<typename T>inline void _output2(T t){for(lint i=0;i<t.size();i++)output(t[i]);}
#define rep(i,n) for(lint i=0;i<lint(n);++i)
#define repi(i,a,b) for(lint i=lint(a);i<(lint)(b);++i)
#define rrep(i,n) for(lint i=lint(n)-1;i>=0;--i)
#define rrepi(i,a,b) for(lint i=lint(b)-1;i>=lint(a);--i)
#define irep(i) for(lint i=0;;++i)
#define all(n) begin(n),end(n)
#define dist(a,b,c,d) sqrt(pow(a-c,2)+pow(b-d,2))
inline lint gcd(lint A,lint B){return B?gcd(B,A%B):A;}
inline lint lcm(lint A,lint B){return A/gcd(A,B)*B;}
// inline cint cgcd(cint A,cint B){return B?cgcd(B,A%B):A;}
// inline cint clcm(cint A,cint B){return A/cgcd(A,B)*B;}
bool chmin(auto& s,const auto& t){bool res=s>t;s=min(s,t);return res;}
bool chmax(auto& s,const auto& t){bool res=s<t;s=max(s,t);return res;}
const vector<lint> dx={1,0,-1,0,1,1,-1,-1};
const vector<lint> dy={0,1,0,-1,1,-1,1,-1};
#define SUM(v) accumulate(all(v),0LL)
auto call=[](auto f,auto... args){return f(f,args...);};

template<typename T>
struct AVL_BASE{
    struct node{
        T val;
        int sz=1,dep=1;
        node* ch[2]={0,0};
        node(T val):val(val){}
        void cpy(node* t){val=t->val;}
    };
    using np=node*;
    int sz(np t){return t?t->sz:0;}
    int dep(np t){return t?t->dep:0;}
    np root=0;
    np update(np t){
        t->sz=sz(t->ch[0])+1+sz(t->ch[1]);
        return t;
    }
    np merge_with_root(np s,np t,np u){
        if(abs(sz(s)-sz(u))<2){
            t->ch[0]=s;t->ch[1]=u;
            return update(t);
        }
        if(sz(s)>sz(u)){
            s->ch[1]=merge_with_root(s->ch[1],t,u);
            return update(s);
        }else{
            u->ch[0]=merge_with_root(s,t,u->ch[0]);
            return update(u);
        }
    }
    np make_root(np& t){
        if(t->ch[1]){
            np res=make_root(t->ch[1]);
            update(t);
            return res;
        }
        else {
            np res=t;
            t=t->ch[0];
            return res;
        }
    }
    np merge(np s,np t){
        if(!s||!t)return s?s:t;
        np u=make_root(s);
        return merge_with_root(s,u,t);
    }
    pair<np,np>split(np t,int i){
        if(!t)return make_pair(nullptr,nullptr);
        np s=t->ch[0],u=t->ch[1];
        t->ch[0]=0;t->ch[1]=0;
        if(i==sz(s)){
            return make_pair(s,merge_with_root(0,t,u));
        }
        if(i<sz(s)){
            auto r=split(s,i);
            return make_pair(r.first,merge_with_root(r.second,t,u));
        }else{
            auto r=split(u,i-sz(s)-1);
            return make_pair(merge_with_root(s,t,r.first),r.second);
        }
    }
    public:
    int size(){return sz(root);}
    void insert(int x,T v){
        assert(0<=x&&x<=size());
        auto s=split(root,x);
        root=merge_with_root(s.first,new node(v),s.second);
    }
    void erase(int x){
        assert(0<=x&&x<size());
        auto s=split(root,x);
        auto t=split(s.second,1);
        root=merge(s.first,t.second);
    }
    T sum(T l,T r){

    }
};

template<typename T>
struct AVL_array:AVL_BASE<T>{
    using AVL_BASE<T>::AVL_BASE;
    void push_back(T v){this->insert(this->size(),v);}
    void pop_back(){this->erase(this->size()-1);}
};

template<typename E=lint,typename T=double>
vector<T> dij(vector<vector<pair<E,T>>> list,lint s,T inf){
    std::priority_queue<pair<T,E>,vector<pair<T,E>>,greater<pair<T,E>>>que;
    vector<T>diff(list.size(),inf);
    diff[s]=0;
    que.push(make_pair(T(),s));
    while(!que.empty()){
        auto d=que.top();
        que.pop();
        T x;E now;
        tie(x,now)=d;
        for(auto d2:list[now]){
            T sa;E to;
            tie(to,sa)=d2;
            if(chmin(diff[to],diff[now]+sa))que.emplace(diff[to],to);
        }
    }
    return diff;
}

int main(){
    lint n,m;
    cin>>n>>m;
    vector<vector<pair<lint,lint>>> v(n+m);
    vector<map<lint,vec>> g(n);
    rep(i,m){
        lint s,t,c;
        cin>>s>>t>>c;
        s--;t--;
        v[s].emplace_back(n+i,1);
        v[n+i].emplace_back(s,1);
        v[t].emplace_back(n+i,1);
        v[n+i].emplace_back(t,1);
        g[s][c].push_back(n+i);
        g[t][c].push_back(n+i);
    }
    rep(i,n)for(auto e:g[i])rep(j,e.second.size()-1){
        v[e.second[j]].emplace_back(e.second[j+1],0);
        v[e.second[j+1]].emplace_back(e.second[j],0);
    }
    auto d=dij(v,0,INF);
    if(d[n-1]==INF)cout<<-1<<endl;
    else cout<<d[n-1]/2<<endl;
}

Measured memory_bytes: 106224