3 3
1 2 1
1 3 2
2 3 4
1 3
2 3 2
0 100

3
?

//考查知识点：克鲁斯卡尔算法
#include<stdio.h>
#include<string.h>
#include<algorithm>
using namespace std;
struct node{
	int sta,end,wei;
}s[110];
int n,m;
int father[110];
int cmp(node x,node y)
{
	return x.wei<y.wei;
}
int find(int x)
{
	int r=x;
	while(r!=father[r])
	r=father[r];
	int j=x;
	while(j!=r)
	{
		int k=father[j];
		father[j]=r;
		j=k;
	}
	return r;
}
//int find(int x)
//{
//	return x==father[x]?x:find(father[x]); 
//}
void kruskal()
{
	int i,j;
	int count=1;
	int sum=0;
	for(i=1;i<=n;++i)
	{
		int fa=find(s[i].sta);
		int fb=find(s[i].end);
		if(fa!=fb)
		{
			father[fa]=fb;
			sum+=s[i].wei;
			count++;
		}
	}
	if(count==m)
	printf("%d\n",sum);
	else
	printf("?\n");
}
int main()
{
	int i,j;
	while(~scanf("%d%d",&n,&m),n)
	{
		for(i=1;i<=m;++i)
		father[i]=i;
		for(i=1;i<=n;++i)
		{
			scanf("%d%d%d",&s[i].sta,&s[i].end,&s[i].wei);
		}
		sort(s+1,s+n+1,cmp);
		kruskal();
	}
	return 0;
}