#include<bits/stdc++.h>

using namespace std;

#define maxn 200005

#define INF 0x3f3f3f3f

struct Edge{

    int to,nxt,w,flag;

}edge[maxn<<];

int head[maxn],tot,n,m;

void init(){memset(head,-,sizeof head);tot=;}

void add(int u,int v,int w){

    edge[tot].to=v;edge[tot].w=w;edge[tot].nxt=head[u];head[u]=tot++;

    edge[tot].flag=;

}

queue<int>q;

int d[maxn];

void dfs(int u,int c,int deep){

    if(d[u]>deep){

        d[u]=deep;

        q.push(u);

    }

    for(int i=head[u];i!=-;i=edge[i].nxt){

        if(edge[i].flag)continue;

        if(edge[i].w==c){

            edge[i].flag=;

            dfs(edge[i].to,c,deep);

        }

    }

}

void bfs(){

    while(q.size())q.pop();

    memset(d,0x3f,sizeof d);

    q.push();

    d[]=;

    while(q.size()){

        int u=q.front();q.pop();

        for(int i=head[u];i!=-;i=edge[i].nxt){

            if(edge[i].flag)continue;

            int v=edge[i].to;

            edge[i].flag=;

            dfs(v,edge[i].w,d[u]+);

        }

    }

}

int main(){

    while(cin>>n>>m){

        memset(edge,,sizeof edge);

        init();

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

            int u,v,w;

            scanf("%d%d%d",&u,&v,&w);

            add(u,v,w);add(v,u,w);

        }

        bfs();

        if(d[n]==INF)puts("-1");

        else cout<<d[n]<<"\n";

    }

}