1 #include<cstdio>
 2 #include<cstring>
 3 #include<stdlib.h>
 4 #include<algorithm>
 5 using namespace std;
 6 const int MAXN=100+10;
 7 struct node
 8 {
 9     int star;
10     int en;
11     int val;
12     bool operator <(const node &B)const
13     {
14         return val<B.val;
15     }
16 }a[MAXN];
17 int p[MAXN];
18 int Find(int x)
19 {
20     return p[x]==x?x:p[x]=Find(p[x]);
21 }
22 int main()
23 {
24     //freopen("in.txt","r",stdin);
25     int n,m;
26     while(scanf("%d %d",&n,&m)&&n)
27     {
28         int ans=0,cnt=0;
29        for(int i=1;i<=n;i++)
30             scanf("%d %d %d",&a[i].star,&a[i].en,&a[i].val);
31        sort(a+1,a+n+1);
32        for(int i=1;i<=m;i++) p[i]=i;
33        for(int i=1;i<=n;i++)
34        {
35             int x=Find(a[i].star);
36             int y=Find(a[i].en);
37             if(x!=y)
38             {               
39                 cnt++;
40                 ans+=a[i].val; 
41                 if(cnt==m-1)
42                     break;
43                 p[x]=y;
44             }
45        }
46        if(cnt==m-1)
47             printf("%d\n",ans);
48        else
49             printf("?\n");
50     }
51     return 0;
52 }