1 #include <iostream>
  2 #include <cstdio>
  3 #include <cstring>
  4 #include <queue>
  5 #define N 1005
  6 #define M 50005
  7 #define INF 0x3f3f3f3f
  8 using namespace std;
  9 
 10 struct Edge
 11 {
 12     int from,to,val;
 13     int next;
 14     bool used;
 15 } edge[M*2];
 16 
 17 int n,m,tol;
 18 int head[M*2],dis[N];
 19 bool vis[N];
 20 int flag;
 21 int path[N];
 22 
 23 void init()
 24 {
 25     tol=0;
 26     flag=0;
 27     memset(head,-1,sizeof(head));
 28     memset(path,-1,sizeof(path));
 29 }
 30 
 31 void addEdge(int u,int v,int val)
 32 {
 33     edge[tol].from=u;
 34     edge[tol].to=v;
 35     edge[tol].val=val;
 36     edge[tol].used=true;
 37     edge[tol].next=head[u];
 38     head[u]=tol++;
 39     edge[tol].from=v;
 40     edge[tol].to=u;
 41     edge[tol].val=val;
 42     edge[tol].used=true;
 43     edge[tol].next=head[v];
 44     head[v]=tol++;
 45 }
 46 
 47 void getmap()
 48 {
 49     scanf("%d%d",&n,&m);
 50     int a,b,c;
 51     while(m--)
 52     {
 53         scanf("%d%d%d",&a,&b,&c);
 54         addEdge(a,b,c);
 55     }
 56 }
 57 
 58 int spfa()
 59 {
 60     memset(dis,INF,sizeof(dis));
 61     memset(vis,false,sizeof(vis));
 62     queue<int>q;
 63     q.push(1);
 64     dis[1]=0;
 65     vis[1]=true;
 66     while(!q.empty())
 67     {
 68         int u=q.front();
 69         q.pop();
 70         vis[u]=false;
 71         for(int i=head[u]; i!=-1; i=edge[i].next)
 72         {
 73             int v=edge[i].to;
 74             if(edge[i].used)
 75                 if(dis[v]>dis[u]+edge[i].val)
 76                 {
 77                     dis[v]=dis[u]+edge[i].val;
 78                     if(!flag)
 79                         path[v]=i;   ///记录可以缩进的边，这些边可以改变总路程
 80                     if(!vis[v])
 81                     {
 82                         vis[v]=true;
 83                         q.push(v);
 84                     }
 85                 }
 86         }
 87     }
 88     return dis[n];
 89 }
 90 
 91 void newmap()
 92 {
 93     int i=n,j=-1;
 94     int ans=-1;
 95     while(path[i]!=-1)
 96     {
 97         j=path[i];
 98         edge[j].used=edge[j+1].used=false;
 99         int tmp=spfa();
100         edge[j].used=edge[j+1].used=true;
101         if(tmp>ans)
102             ans=tmp;
103         i=edge[j].from;
104     }
105     if(ans<INF)
106         printf("%d\n",ans);
107     else
108         printf("-1\n");
109 }
110 
111 int main()
112 {
113     int T;
114     scanf("%d",&T);
115     while(T--)
116     {
117         init();
118         getmap();
119         spfa();
120         newmap();
121     }
122 }