1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<queue>
 5 #include<map>
 6 #define M 1000010
 7 using namespace std;
 8 int read()
 9 {
10     char ch=getchar();int x=0;
11     while(ch>'9'||ch<'0') ch=getchar();
12     while(ch>='0'&&ch<='9') x=x*10+ch-'0',ch=getchar();
13     return x;
14 }
15 struct point{
16     int to,next,dis;
17 }e[M<<1];
18 int n,m,num,cnt;
19 int head[M],dis[M];bool vis[M];
20 void add(int from,int to,int dis)
21 {
22     e[++num].next=head[from];
23     e[num].to=to;
24     e[num].dis=dis;
25     head[from]=num;
26 }
27 void SPFA()
28 {
29     memset(dis,127,sizeof(dis));
30     queue<int>q;
31     q.push(1);
32     vis[1]=true;
33     dis[1]=0;
34     while(!q.empty())
35     {
36         int x=q.front(); q.pop();
37         for(int i=head[x];i;i=e[i].next)
38         {
39             int to=e[i].to;
40             if(dis[to]>dis[x]+e[i].dis)
41             {
42                 dis[to]=dis[x]+e[i].dis;
43                 if(!vis[to])
44                 {
45                     vis[to]=true;
46                     q.push(to);
47                 }
48             }
49         }
50         vis[x]=false;
51     }
52 }
53 map<pair<int,int>,int>P;
54 int get(int x,int y)
55 {
56     if(P.find(make_pair(x,y))!=P.end()) return P[make_pair(x,y)];
57     else return P[make_pair(x,y)]=++cnt;
58 }
59 int main()
60 {
61     n=cnt=read(); m=read();
62     for(int i=1;i<=m;i++)
63     {
64         int a=read(),b=read(),c=read();
65         int id1=get(a,c),id2=get(b,c);
66         add(id1,id2,0); add(id2,id1,0);
67         add(a,id1,1); add(id1,a,1);
68         add(b,id2,1); add(id2,b,1);
69     }
70     SPFA();
71     printf("%d\n",dis[n]>2*n?-1:dis[n]/2);
72     return 0;
73 }