// Slower C++ solution:
#include <stdio.h>

#include <string.h>

#include <algorithm>

#define ME 200000

#define MN 1400000

#define INF 0x7f7f7f7f

int n,m,pl,ql,pc;

int lst[MN+5],pnt[MN+5];

int dis[MN+5]; bool usd[MN+5];

int hd[MN+5],to[MN+5],val[MN+5],nxt[MN+5],rn=0;

struct edge{int p,q,c;}e[ME+5];

bool cmp(edge a,edge b){return a.c<b.c;}

struct DEQUE{

	int mem[MN*2+5],hd,tl;

	DEQUE(){hd=MN,tl=MN+1;}

	int front(){return mem[hd];}

	bool empty(){return hd==tl-1;}

	void hdpush(int x){mem[++hd]=x;}

	void hdpop(){--hd;}

	void tlpush(int x){mem[--tl]=x;}

	void tlpop(){++tl;}

}q;

inline void add(int u,int v,int c){

	++rn;

	nxt[rn]=hd[u],hd[u]=rn;

	to[rn]=v,val[rn]=c;

}

int main(){

	memset(dis,0x7f,sizeof(dis));

	memset(hd,0xff,sizeof(hd));

	scanf("%d%d",&n,&m); pc=n;

	for(int i=1;i<=m;i++)

		scanf("%d%d%d",&e[i].p,&e[i].q,&e[i].c);

	std::sort(e+1,e+1+m,cmp);

	for(int i=1;i<=m;i++){

		if(lst[e[i].p]!=e[i].c){

			lst[e[i].p]=e[i].c,pnt[e[i].p]=(++pc);

			add(e[i].p,pnt[e[i].p],1),add(pnt[e[i].p],e[i].p,0);

		}

		if(lst[e[i].q]!=e[i].c){

			lst[e[i].q]=e[i].c,pnt[e[i].q]=(++pc);

			add(e[i].q,pnt[e[i].q],1),add(pnt[e[i].q],e[i].q,0);

		}

		add(pnt[e[i].p],pnt[e[i].q],0),add(pnt[e[i].q],pnt[e[i].p],0);

	}

	dis[1]=0; q.tlpush(1);

	for(int d=0;;d++){

		while(1){

			int u=q.front();

			if(usd[u]){q.hdpop();continue;}

			if(dis[u]!=d)break;

			q.hdpop(); usd[u]=true;

			for(int i=hd[u];i!=-1;i=nxt[i]){

				if(!usd[to[i]]){

					if(val[i]==0){

						if(dis[to[i]]>d){

							dis[to[i]]=d;

							q.hdpush(to[i]);

						}

					}else{

						if(dis[to[i]]>d+1){

							dis[to[i]]=d+1;

							q.tlpush(to[i]);

						}

					}

				}

			}

		}

		if(dis[n]!=INF||q.empty())break;

	}

	printf("%d",dis[n]==INF?-1:dis[n]);

}

// Faster C++ solution for the same problem (measured speedup: 1.772319393992342x):
#include<iostream>

#include<cstdio>

#include<cstring>

#include<climits>

#include<algorithm>

#include<cmath>

#include<queue>

#include<map>

#include<set>

using namespace std;

#define MAXN 100000

#define MAXM 200000

#define INF INT_MAX

int n,m;

struct node

{

    int next,to,w;

}e[MAXM*2+5];

int b[MAXN+5];

int x,y,z,cnt,s,t,ans;

map<int,int> Ncolor[MAXN+5];

int dist[MAXN+5];

priority_queue < pair<int,int> > Q;

void fpush(int u,int v,long long w)

{

    e[++cnt].next=b[u];

    e[cnt].w=w;

    e[cnt].to=v;

    b[u]=cnt;

}

void Dijkstra()

{

     Q.push({0,s});

    dist[s]=1;

    while(!Q.empty())

    {

        int now=Q.top().second,xval=-Q.top().first;

        Q.pop();

        for(int i=b[now];i;i=e[i].next)

        {

            int xnext=e[i].to,color=e[i].w;

            int val=xval;

            if(!Ncolor[now].count(color))val++;

            if(dist[xnext]>val)

            {

                Ncolor[xnext].clear();

                Ncolor[xnext][color]=1;

                dist[xnext]=val;

                Q.push({-val,xnext});

            }

            if(dist[xnext]==val)Ncolor[xnext][color]=1;

        }

    }

}

int main()

{

    fill(dist+1,dist+MAXN+1,INF);

    scanf("%d%d",&n,&m);

    s=1,t=n;

    for(int i=1;i<=m;i++)

    {

        scanf("%d%d%d",&x,&y,&z);

        fpush(x,y,z);

        fpush(y,x,z);

    }

    Dijkstra();

    if(dist[n]!=INF)printf("%d",dist[n]);

    else printf("-1");

}