/*

     此题为：HDOJ 1233 + HDOJ 1232

 */

 #include <cstdio>

 #include <algorithm>

 #include <cstring>

 #include <cmath>

 using namespace std;

 const int MAX_N =  + ;

 int pre[MAX_N];

 int tot;

 int sum;

 struct NODE

 {

     int x, y;

     int len;

 }node[MAX_N];

 int find(int root)

 {

     int son, tmp;

     son = root;

     while (root != pre[root])

     {

         root = pre[root];

     }

     while (son != root)

     {

         tmp = pre[son];

         pre[son] = root;

         son = tmp;

     }

     return root;

 }

 bool cmp(NODE a, NODE b)

 {

     return a.len < b.len;

 }

 int main(void)        //HDOJ 1863 畅通工程

 {

     //freopen ("inC.txt", "r", stdin);

     int n, m;        //n路， m村庄

     while (~scanf ("%d%d", &n, &m) && n)

     {

         tot = m - ;

         for (int i=; i<=m; ++i)

         {

             pre[i] = i;

         }

         for (int i=; i<=n; ++i)

         {

             scanf ("%d%d%d", &node[i].x, &node[i].y, &node[i].len);

         }

         sort (node+, node++n, cmp);

         sum = ;

         for (int i=; i<=n; ++i)

         {

             int a, b;

             a = find (node[i].x);

             b = find (node[i].y);

             if (a != b)

             {

                 pre[a] = b;

                 sum += node[i].len;

                 --tot;

             }

         }

         if (tot == )

             printf ("%d\n", sum);

         else

             puts ("?");

     }

 }