RT

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll MAXN=2e6;
ll t,n,m,x,y,z;
struct Graph{
	struct edge{
		ll u,v,w,nxt;
	}e[MAXN];
	ll head[MAXN],edge_num;
	ll dfn[MAXN],low[MAXN],cnt,st[MAXN],top,scc[MAXN];
	bool in_stack[MAXN];
	void init(ll N,ll M){
		for(int i=1;i<=N;i++)head[i]=dfn[i]=low[i]=st[i]=scc[i]=in_stack[i]=0;
		for(int i=1;i<=(M<<2);i++)e[i]=(edge){0,0,0,0};
		edge_num=cnt=top=0;
		return;
	}
	void add_edge(ll From,ll To,ll Len){
		edge_num++;
//		cout<<"debug "<<From<<" "<<To<<" "<<Len<<" "<<head[From]<<'\n';
		e[edge_num]=(edge){From,To,Len,head[From]};
		head[From]=edge_num;
		return;
	}
	void tarjan(ll now){
		dfn[now]=low[now]=++cnt,st[++top]=now,in_stack[now]=1;
		for(int i=head[now];i;i=e[i].nxt){
			if(!dfn[e[i].v]){
				tarjan(e[i].v);
				low[now]=min(low[now],low[e[i].v]);
			}
			else if(in_stack[e[i].v])low[now]=min(low[now],dfn[e[i].v]);
		}
		if(dfn[now]==low[now]){
			ll pos;
			while(pos=st[top--]){
				scc[pos]=now;
				in_stack[now]=0;
				if(pos==now)break;
			}
		}
		return;
	}
}G,tmp,dag;
ll fa[MAXN];
ll Find(ll num){
	return fa[num]==num?num:fa[num]=Find(fa[num]);
}
ll in[MAXN];
bool check(ll num){
	tmp=G;
	for(int i=1;i<=G.edge_num;i++)if(tmp.e[i].w<=num)tmp.add_edge(tmp.e[i].v,tmp.e[i].u,tmp.e[i].w);
	for(int i=1;i<=n;i++)if(!tmp.dfn[i])tmp.tarjan(i);
	for(int i=1;i<=n;i++)in[i]=0;
	dag.init(n,m);
	for(int i=1;i<=tmp.edge_num;i++){
		if(tmp.scc[tmp.e[i].u]==tmp.scc[tmp.e[i].v])continue;
		in[tmp.scc[tmp.e[i].v]]++;
	}
	ll pos=0;
	for(int i=1;i<=n;i++){
		if(i!=tmp.scc[i])continue;
		if(in[i]==0){
			if(pos)return 0;
			pos=i;
		}
	}
	return pos;
}
int main(){
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0); 
	cin>>t;
	while(t--){
		cin>>n>>m;
		G.init(n,m);
		for(int i=1;i<=n;i++)fa[i]=i;
		ll L=0,R=0,mid;
		for(int i=1;i<=m;i++){
			cin>>x>>y>>z;
			G.add_edge(x,y,z);
			fa[Find(x)]=Find(y);
			R=max(R,z);
		}
		bool fl=0;
		for(int i=2;i<=n;i++)if(Find(i)!=Find(1)){
			fl=1;
			break;
		}
		if(fl==1){
			cout<<"-1\n";
			continue;
		} 
		while(L<=R){
			mid=(L+R)>>1;
			if(check(mid))R=mid-1;
			else L=mid+1;
		}
		cout<<L<<'\n';
	}
	return 0;
}