样例没过，贪心蒜法无并查集显然是错的，样例没过，AC了……

#include<bits/stdc++.h>
using namespace std;
const int N=1e5+10;
int n,m;
int B[N];
int ans;

class Node{
public:
	int x;
	int y;
	int t;
	bool operator<(Node& b){
		return t<b.t;
	}
}a[N];

int main(){
	cin>>n>>m;
	for(int i=1;i<=m;i++){
		cin>>a[i].x>>a[i].y>>a[i].t;
	}
	sort(a+1,a+m+1);
	for(int i=1;i<=m;i++){
		if(B[a[i].x]==0) ans++,B[a[i].x]=1;
		if(B[a[i].y]==0) ans++,B[a[i].y]=1;
		if(ans>=n) {
			cout<<a[i].t;
			return 0;
		}
	}
	cout<<"-1";
	return 0;
}