样例不过+WA0分，玄关求条，码风良好

#include <bits/stdc++.h>
using namespace std;
int n, m, a[100005], b[100005], c[100005], l = INT_MAX, r = -1, fa[20005];
int Find(int root) {
	if(fa[root]==root) return root;
	return fa[root] = Find(fa[root]);
}
void merge(int x, int y) {
	int fx = Find(x), fy = Find(y);
	if(fx!=fy) fa[fy] = fx;
}
bool check(int x) {
	for(int i=1; i<=n; i++) fa[i] = i;
	for(int i=1; i<=m; i++)
		if(c[i]<=x) merge(a[i], b[i]);
	int cnt = 0;
	for(int i=1; i<=n; i++)
		if(fa[i]==i) cnt ++;
	return cnt<=2;
}
int main() {
    scanf("%d %d", &n, &m);
    if(m==0) {
    	printf("0");
    	return 0;
	}
    for(int i=1; i<=m; i++) {
    	scanf("%d %d %d", &a[i], &b[i], &c[i]);
    	l = min(l, c[i]), r = max(r, c[i]);
	}
	while(l<=r) {
		int mid = l+r>>1;
		if(check(mid)) r = mid-1;
		else l = mid+1;
	}
	printf("%d", l);
    return 0;
}