#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define pb push_back
#define mp make_pair
#define all(a) begin(a),end(a)
#define FOR(x,val,to) for(int x=(val);x<int((to));++x)
#define FORE(x,val,to) for(auto x=(val);x<=(to);++x)
#define FORR(x,arr) for(auto &x: arr)
#define FORS(x,plus,arr) for(auto x = begin(arr)+(plus); x != end(arr); ++x)
#define FORREV(x,plus,arr) for(auto x = (arr).rbegin()+(plus); x !=(arr).rend(); ++x)
#define REE(s_) {cout<<s_<<'\n';exit(0);}
#define GET(arr) for(auto &i: (arr)) sc(i)
#define whatis(x) cerr << #x << " is " << (x) << endl;
#define e1 first
#define e2 second
#define INF 0x7f7f7f7f
typedef std::pair<int,int> pi;
typedef std::vector<int> vi;
typedef std::vector<std::string> vs;
typedef int64_t ll;
typedef uint64_t ull;
#define umap unordered_map
#define uset unordered_set
using namespace std;
using namespace __gnu_pbds;

#ifdef _WIN32
#define getchar_unlocked() _getchar_nolock()
#define _CRT_DISABLE_PERFCRIT_LOCKS
#endif
template<class L, class R> ostream& operator<<(ostream &os, map<L, R> P) { for(auto const &vv: P)os<<"("<<vv.first<<","<<vv.second<<")"; return os; }
template<class T> ostream& operator<<(ostream &os, set<T> V) { os<<"[";for(auto const &vv:V)os<<vv<<","; os<<"]"; return os; }
template<class T> ostream& operator<<(ostream &os, vector<T> V) { os<<"[";for(auto const &vv:V)os<<vv<<","; os<<"]"; return os; }
template<class L, class R> ostream& operator<<(ostream &os, pair<L, R> P) { os<<"("<<P.first<<","<<P.second<<")"; return os; }
inline int fstoi(const string &str){auto it=str.begin();bool neg=0;int num=0;if(*it=='-')neg=1;else num=*it-'0';++it;while(it<str.end()) num=num*10+(*it++-'0');if(neg)num*=-1;return num;}
inline void getch(char &x){while(x = getchar_unlocked(), x < 33){;}}
inline void getstr(string &str){str.clear(); char cur;while(cur=getchar_unlocked(),cur<33){;}while(cur>32){str+=cur;cur=getchar_unlocked();}}
template<typename T> inline bool sc(T &num){ bool neg=0; int c; num=0; while(c=getchar_unlocked(),c<33){if(c == EOF) return false;} if(c=='-'){ neg=1; c=getchar_unlocked(); } for(;c>47;c=getchar_unlocked()) num=num*10+c-48; if(neg) num*=-1; return true;}template<typename T, typename ...Args> inline void sc(T &num, Args &...args){ bool neg=0; int c; num=0; while(c=getchar_unlocked(),c<33){;} if(c=='-'){ neg=1; c=getchar_unlocked(); } for(;c>47;c=getchar_unlocked()) num=num*10+c-48; if(neg) num*=-1; sc(args...); }
template<typename T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>; //s.find_by_order(), s.order_of_key() <- works like lower_bound
template<typename T> using ordered_map = tree<T, int, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
#define N 1000001

int main(){
    ios_base::sync_with_stdio(0);cin.tie(0);
    int n,m;
    sc(n,m);
    pair<int,set<int>> dp[n]; //{min cs, which carrers}
    map<int,vi> adj[n];
    FOR(i,0,m){
        int f,s,w;
        sc(f,s,w);
        --f,--s,--w;
        adj[f][w].pb(s);
        adj[s][w].pb(f);
    }
    priority_queue<array<int,3>> pq;
    FORR(i,dp)
        i.e1 = INF;
    dp[0].e1 = 1;
    FORR(i,adj[0]){
        pq.push({-1,0,i.e1});
        dp[0].e2.insert(i.e1);
    }
    int nmn[n];
    memset(nmn,127,n<<2);
    while(!pq.empty()){
        int w = -pq.top()[0];
        int v = pq.top()[1];
        int car = pq.top()[2];
        /* whatis(w) */
        /* whatis(v+1) */
        /* whatis(car+1) */
        pq.pop();
        if(w != dp[v].e1) continue;
        if(w == nmn[v]){ //new min
            nmn[v] = INF;
            FORR(i,adj[v]){
                FORR(x,i.e2){
                    int neww = w+(i.e1 != car);
                    if(neww < dp[x].e1){
                        dp[x].e1 = neww;
                        dp[x].e2 = {i.e1};
                        nmn[x] = neww;
                        pq.push({-neww,x,i.e1});
                    }
                    else if(neww == dp[x].e1 && dp[x].e2.insert(i.e1).e2){
                        pq.push({-neww,x,i.e1});
                    }
                }
            }
        }
        else{
            FORR(x,adj[v][car]){
                if(w < dp[x].e1){
                    dp[x].e1 = w;
                    dp[x].e2 = {car};
                    nmn[x] = w;
                    pq.push({-w,x,car});
                }
                else if(w == dp[x].e1 && dp[x].e2.insert(car).e2){
                    pq.push({-w,x,car});
                }
            }
        }
    }
    int ans = dp[n-1].e1;
    if(ans == INF) ans = -1;
    cout << ans << '\n';
}



Measured memory_bytes: 64564