#include <cstdio>
#include <algorithm>
#include <cstring>
#define MAX 110
#define INF 1000000000
using namespace std ;

struct Edge{
	int x,y,w;
}edge[MAX];
int f[MAX] ;

bool cmp(const Edge &a ,const Edge &b)
{
	return a.w<b.w ;
}

void init()
{
	for(int i = 0 ; i < MAX; ++i)
	{
		f[i] = i ; 
	}
}
int find(int x)
{
	int r = x ;
	while(r != f[r])
	{
		r = f[r] ;
	}
	int temp ;
	while(x != r)
	{
		temp = f[x] ;
		f[x] = r ;
		x = temp ;
	}
	return r ;
}

int kruskal(int n , int m)
{
	int lowcost[MAX];
	bool visited[MAX] ;
	memset(visited,false,sizeof(visited)) ;
	sort(edge,edge+n,cmp);
	for(int i = 0 ; i <= m ; ++i)
	{
		lowcost[i] = INF ;
	}
	int index = 0 ;
	init() ;
	for(int i = 0 ; i < n ; ++i)
	{
		int fx = find(edge[i].x) , fy = find(edge[i].y) ;
		if(fx != fy)
		{
			lowcost[index++] = edge[i].w ;
			f[fx] = fy ;
		}
	}
	int sum = 0 ;
	for(int i = 0 ; i < m-1 ; ++i)
	{
		if(lowcost[i] == INF)
		{
			return INF ;
		}
		else
		{
			sum += lowcost[i] ;
		}
	}
	return sum ;
}

int main()
{
	int n , m ;
	while(~scanf("%d%d",&n,&m) && n)
	{
		for(int i = 0 ; i < n ; ++i)
		{
			int x , y , w ;
			scanf("%d%d%d",&x,&y,&w) ;
			edge[i].x = x ;
			edge[i].y = y ;
			edge[i].w = w ;
		}
		int sum = kruskal(n,m) ;
		if(sum == INF)
		{
			puts("?");
		}
		else
		{
			printf("%d\n",sum) ;
		}
	}
	return 0 ;
}

#include <stdio.h>
#include <string.h>
#define MAX 110
#define INF 1000000000

int graph[MAX][MAX] ,visited[MAX] ;

int prim(int m)
{
	int lowcost[MAX] , closest[MAX];
	for(int i = 1 ; i <= m ; ++i)
	{
		closest[i] = 1 ;
		lowcost[i] = graph[1][i] ;
	}
	lowcost[1] = 0 ;
	memset(visited,false,sizeof(visited)) ;
	visited[1] = true ; 
	for(int i = 0 ; i < m-1 ; ++i)
	{
		int min = INF , index=0 ;
		for(int j = 1 ; j <= m ; ++j)
		{
			if(!visited[j] && lowcost[j]<min)
			{
				min = lowcost[j] ;
				index=j ;
			}
		}
		visited[index] = true ;
		for(int j = 1 ; j <= m ; ++j)
		{
			if(!visited[j] && lowcost[j]>graph[index][j])
			{
				lowcost[j] = graph[index][j] ;
				closest[j] = index ;
			}
		}
	}
	int sum = 0 ;
	for(int i = 1 ; i <= m ; ++i)
	{
		if(lowcost[i] == INF)
		{
			return INF ;
		}
		sum += lowcost[i] ;
	}
	return sum ;
}

int main()
{
	int n , m ;
	while(~scanf("%d%d",&n,&m) && n)
	{
		for(int i = 0 ; i <= m ; ++i)
		{
			for(int j = 0 ; j <= i ; ++j)
			{
				graph[i][j] = graph[j][i] = INF ;
			}
		}
		for(int i = 0 ; i < n ; ++i)
		{
			int x , y , w ;
			scanf("%d%d%d",&x,&y,&w);
			graph[x][y] = graph[y][x] = w ;
		}
		int sum = prim(m) ;
		if(sum == INF)
		{
			puts("?");
		}
		else
		{
			printf("%d\n",sum) ;
		}
	}
	return 0 ;
}