#pragma comment(linker, "/stack:200000000")
#pragma GCC optimize("Ofast")
#pragma GCC optimize(3)
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#pragma GCC target("sse3","sse2","sse")
#pragma GCC target("avx","sse4","sse4.1","sse4.2","ssse3")
#pragma GCC target("f16c")
#pragma GCC optimize("inline","fast-math","unroll-loops","no-stack-protector")
#pragma GCC diagnostic error "-fwhole-program"
#pragma GCC diagnostic error "-fcse-skip-blocks"
#pragma GCC diagnostic error "-funsafe-loop-optimizations"
#pragma GCC diagnostic error "-std=c++14"
#include "bits/stdc++.h"
//#include "ext/pb_ds/tree_policy.hpp"
//#include "ext/pb_ds/assoc_container.hpp"
#define PB push_back
#define PF push_front
#define LB lower_bound
#define UB upper_bound
#define fr(x) freopen(x,"r",stdin)
#define fw(x) freopen(x,"w",stdout)
#define iout(x) printf("%d\n",x)
#define lout(x) printf("%lld\n",x)
#define REP(x,l,u) for(ll x = l;x<u;x++)
#define RREP(x,l,u) for(ll x = l;x>=u;x--)
#define complete_unique(a) a.erase(unique(a.begin(),a.end()),a.end())
#define mst(x,a) memset(x,a,sizeof(x))
#define all(a) a.begin(),a.end()
#define PII pair<int,int>
#define PLL pair<ll,ll>
#define MP make_pair
#define sqr(x) ((x)*(x))
#define lowbit(x) (x&(-x))
#define lson (ind<<1)
#define rson (ind<<1|1)
#define se second
#define fi first
#define dbg(x) cerr<<#x<<" = "<<(x)<<endl;
#define sz(x) ((int)x.size())
#define EX0 exit(0);

typedef  long long ll;
typedef unsigned long long ull;
typedef double db;
typedef long double ld;
using namespace std;
typedef vector<ll> VLL;
typedef vector<int> VI;
const int block_size = 320;
typedef complex<ll> point;
const ll mod = 1e9+7;
const ll inf = 1e9+7;
const ld eps = 1e-9;
const db PI = atan(1)*4;
template<typename T>
inline int sign(const T&a) {
    if(a<0)return -1;
    if(a>0)return 1;
    return 0;
}

template<typename T,typename S>inline bool upmin(T&a,const S&b){return a>b?a=b,1:0;}
template<typename T,typename S>inline bool upmax(T&a,const S&b){return a<b?a=b,1:0;}

template<typename T> inline void in(T &x) {
    x = 0;
    T f = 1;
    char ch = getchar();
    while (!isdigit(ch)) {
        if (ch == '-') f = -1;
        ch = getchar();
    }
    while (isdigit(ch))  {
        x = x * 10 + ch - '0';
        ch = getchar();
    }
    x *= f;
}

ll twop(int x) {
    return 1LL<<x;
}

template<typename A,typename B > inline void in(A&x,B&y) {
    in(x);
    in(y);
}
template<typename A,typename B,typename C>inline void in(A&x,B&y,C&z) {
    in(x);
    in(y);
    in(z);
}
template<typename A,typename B,typename C,typename D> inline void in(A&x,B&y,C&z,D&d) {
    in(x);
    in(y);
    in(z);
    in(d);
}
ll gcd(ll a,ll b){return b==0?a:gcd(b,a%b);}
namespace SOLVE {
    void main(){
    }
}


map<int, vector<int>>ed[1000010];
vector<PII>adj[100010];
int n,m;
int dis[100010];
set<PII>vis;
int original;
void dfs(priority_queue<pair<int, PII>,vector<pair<int, PII>>,greater<pair<int, PII>>>&pq,int cur,int color){
    for(auto neighbour:ed[color][cur]){
        if(vis.count(MP(neighbour,color)) == 0){
            if(dis[original]<dis[neighbour])pq.push(MP(dis[original],MP(neighbour,color)));
            vis.insert(MP(neighbour,color));
            dfs(pq, neighbour, color);
        }
    }
}
int main() {

    
    
    
    
    
    in(n,m);
    REP(i,0,m){
        int u,v,w;in(u,v,w);
        ed[w][u].PB(v);
        ed[w][v].PB(u);
        adj[u].PB(MP(v,w));
        adj[v].PB(MP(u,w));
    }
    mst(dis,0x3f);



    priority_queue<pair<int, PII>,vector<pair<int, PII>>,greater<pair<int, PII>>>pq;
    pq.push(MP(0,MP(1,0)));
    while (sz(pq)) {
        auto color = pq.top().se.se,source = pq.top().se.fi,d = pq.top().fi;
        pq.pop();
        if(d<dis[source]){
            dis[source] = d;
            original = source;
            vis.insert(MP(source,color));
            dfs(pq, source, color);
            for(auto neighbor:adj[source]){
                pq.push(MP(d+1,MP(neighbor.fi,neighbor.se)));
            }
        }else if(d == dis[source] && vis.count(MP(source,color)) == 0){
            vis.insert(MP(source,color));
            dfs(pq, source, color);

        }
    }




    if(dis[n]>1000000)cout<<-1;
    else cout<<dis[n];
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    return 0;
}


Measured memory_bytes: 119276