学步园

//kruskal算法
#include<iostream>
#include<string.h>
#include<algorithm>
using namespace std;
typedef struct edge
{
	int v,w,value;
}edge;
edge edges[101];
int father[101];
int childcounts[101];
int cmp(edge a,edge b)
{
	return a.value<b.value;
}
 int findfather(int x)
{
	return father[x]==x?x:findfather(father[x]);
}
int unions(int x,int y)
{
	int rootx=findfather(x);
	int rooty=findfather(y);
	if(rootx==rooty) return 0;
	else if(childcounts[x]>=childcounts[y])
	{
		father[rooty]=rootx;
		childcounts[x]+=childcounts[y];
	}
	else
	{
		father[rootx]=rooty;
		childcounts[y]+=childcounts[x];
	}
	return 1;
}
int main()
{
	int n,m,i,j,a,b,c,num,sum;
    while(cin >> n >> m &&n)
	{
		num=0;sum=0;
		for(i=1;i<=n;i++)
		{
			cin >> edges[i].v >> edges[i].w >> edges[i].value;
		}
		for(i=1;i<=m;i++)
		{
			father[i]=i;
			childcounts[i]=1;
		}
		sort(edges+1,edges+n+1,cmp);
		for(j=1;j<=n;j++)
		{
			if(unions(edges[j].v,edges[j].w))
			{
				num++;
				sum+=edges[j].value;
			}
		}
		if(num==m-1) cout << sum << endl;
		else cout << '?' << endl;
	}
	return 0;
}