#include<bits/stdc++.h>
using namespace std;

const int INF=1e9+10;
const int MAX_N=5e6+10;

pair<int,int> dots[MAX_N];
vector <pair<int,int> > G[MAX_N];
int dist[MAX_N],N,M,n=0,m=0;
vector <pair<int,int> > g[MAX_N];
map <pair<int,int>,int> Map;
priority_queue <pair<int,int> > Q;

int main(){
	cout<<MAX_N<<endl;
	scanf("%d%d",&N,&M);
	for(int i=0;i<M;i++){
		int u,v,c; 
		scanf("%d%d%d",&u,&v,&c);
		u--; v--;
		G[u].push_back(make_pair(v,c));
		G[v].push_back(make_pair(u,c));
	}
	for(int i=0;i<N;i++){
		for(int j=0;j<G[i].size();j++){
			int c=G[i][j].second,fr=G[i][j].first;
			if(Map.find(make_pair(i,c))==Map.end()){
				dots[n].first=i; dots[n].second=c;
				Map[make_pair(dots[n].first,dots[n].second)]=n;
				n++;
			}
		}
	}
	for(int i=0;i<n;i++){
		int u=dots[i].first,c1=dots[i].second;
		for(int j=0;j<G[u].size();j++){
			int v=G[u][j].first,c2=G[u][j].second;
			int to=Map[make_pair(v,c2)];
			if(v!=u){
				if(c1==c2){
					g[i].push_back(make_pair(to,0));
					g[to].push_back(make_pair(i,0));
					m++;
				}
				else{
					g[i].push_back(make_pair(to,1));
					g[to].push_back(make_pair(i,1));
					m++;
				}
			}
		}
	}
	for(int i=0;i<MAX_N;i++) dist[i]=INF;
	for(int i=0;i<G[0].size();i++){
		int st=G[0][i].first,c=G[0][i].second;
		dist[Map[make_pair(st,c)]]=1;
		Q.push(make_pair(-dist[Map[make_pair(st,c)]],Map[make_pair(st,c)]));	
	}
	while(!Q.empty()){
		int x=Q.top().second,val=-Q.top().first;
		Q.pop();
		if(dist[x]<val) continue;
		for(int i=0;i<g[x].size();i++){
			int to=g[x][i].first,cost=g[x][i].second;
			if(dist[to]>dist[x]+cost){
				dist[to]=dist[x]+cost;
				Q.push(make_pair(-dist[to],to));
			}
		}
	}
	int ans=INF;
	for(int i=0;i<n;i++){
		int x=dots[i].first;
		if(x==N-1){
			ans=min(ans,dist[i]);		
		}
	}
	if(ans==INF) printf("-1\n");
	else printf("%d\n",ans);
	return 0;
} 