/* ***********************************************
Author        :devil
Created Time  :2016/6/10 14:20:54
************************************************ */
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <string>
#include <cmath>
#include <stdlib.h>
using namespace std;
const int N=1010;
const int inf=0x3f3f3f3f;
struct node
{int v,d;node(int a=0,int b=0):v(a),d(b){}bool operator < (const node &a) const{return d>a.d;}
};
struct edge
{int v,cost;edge(int a=0,int b=0):v(a),cost(b){}
};
vector<edge> eg[N];
bool vis[N];
int n,m,dis[N],pre[N];
void dijkstra(int x)
{memset(vis,false,sizeof(vis));for(int i=0; i<=n+1; i++)dis[i]=inf;priority_queue<node>q;while(!q.empty()) q.pop();dis[x]=0;q.push(node(x,0));node tmp;while(!q.empty()){tmp=q.top();q.pop();int u=tmp.v;if(vis[u]) continue;vis[u]=1;for(int i=0; i<eg[u].size(); i++){int v=eg[tmp.v][i].v;int cost=eg[u][i].cost;if(!vis[v]&&dis[v]>dis[u]+cost){dis[v]=dis[u]+cost;pre[v]=u;q.push(node(v,dis[v]));}else if(!vis[v]&&dis[v]==dis[u]+cost)pre[v]=min(pre[v],u);}}
}
int main()
{//freopen("in.txt","r",stdin);int t,u,v,w;scanf("%d",&t);while(t--){scanf("%d%d",&n,&m);for(int i=0;i<=n+1;i++)eg[i].clear();while(m--){scanf("%d%d%d",&u,&v,&w);eg[v].push_back(edge(u,w));}dijkstra(n+1);if(dis[0]==inf){printf("-1\n");continue;}if(pre[0]==n+1){printf("0\n");continue;}printf("%d\n",pre[0]);}return 0;
}