#include
    
     #include
     
      int father[105],depth[105];int dist[105],map[101][101];int vis[105],n;void init_B(){    int i;    for(i = 1;i <= n;i ++)    {        father[i] = i;        depth[i] = 0;    }}int find(int x){    if(x == father[x])        return x;    return father[x] = find(father[x]);}void unit(int x,int y){    x = find(x);    y = find(y);    if(x == y)        return ;    if(depth[x] < depth[y])        father[x] = y;    else    {        if(depth[x] > depth[y])            father[y] = x;        else        {            father[x] = y;            depth[y]++;        }    }}void init(){    int i;    memset(vis,0,sizeof(vis));    for(i = 1;i <= n;i ++)        dist[i] = map[1][i];}int main(){    int m,i,j,k,a,b;    int min,cnt,cost,sum;    while(~scanf("%d%d",&m,&n) && m)    {        init_B();        sum = cnt = 0;        for(i = 1;i <= n;i ++)        {            for(j = 1;j <= n;j ++)            {                if(i != j)                {                    map[i][j] = 1 << 30;                }            }        }        while(m--)        {            scanf("%d%d%d",&a,&b,&cost);            map[a][b] = map[b][a] = cost;            unit(a,b);        }        init();        for(i = 1;i <= n;i ++)        {            if(i == find(i))                cnt++;            if(cnt == 2)                break ;        }        if(cnt == 2)        {            printf("?\n");            continue ;        }        for(i = 0;i < n;i ++)        {            min = 1 << 30;            for(j = 1;j <= n;j ++)            {                if(!vis[j] && min > dist[j])                {                    min = dist[j];                    k = j;                }            }            vis[k] = 1;            if(min != 1 << 30)                sum += min;            for(j = 1;j <= n;j ++)            {                if(!vis[j] && dist[j] > map[k][j])                    dist[j] = map[k][j];            }        }        printf("%d\n",sum);    }    return 0;}