#include <iostream>

#include <cmath>

#include <cstring>

#include <cstdlib>

#include <cstdio>

#include <algorithm>

#include <vector>

#include <queue>

using namespace std;

#define INF 0xfffffff

#define maxn 103

struct Edge

{

    int e, w;

    Edge(int e=,int w=): e(e), w(w) {}

    friend bool operator < (Edge A, Edge B)

    {

        return A.w < B.w;

    }

};

vector<Edge> G[maxn];

int dist[maxn];

bool vis[maxn];

int m, n;

int Prime()

{

    Edge P, Pn;

    int Nnode = ;

    dist[] = ;

    priority_queue < Edge > Q;

    Q.push( Edge(,) );

    while( !Q.empty() && Nnode < n )

    {

        while( !Q.empty() )

        {

            P = Q.top();

            Q.pop();

            if( !vis[P.e] )

                break;

        }

        if( vis[P.e] )

            continue;

        Nnode ++;

        vis[P.e] = true;

        int len = G[P.e].size();

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

        {

            Pn = G[P.e][i];

            if(!vis[Pn.e] && dist[Pn.e] > Pn.w)

            {

                dist[Pn.e] = Pn.w;

                Q.push(Pn);

            }

        }

    }

    if(Nnode < n)

        return -;

    int sum = ;

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

    {

        sum += dist[i];

    }

    return sum;

}

void Init()

{

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

    {

        G[i].clear();

        dist[i] = INF;

        vis[i] = false;

    }

}

int main()

{

    while(cin >> m >> n, m)

    {

        Init();

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

        {

            int a, b, c;

            cin >> a >> b >> c;

            G[a].push_back( Edge(b,c) );

            G[b].push_back( Edge(a,c) );

        }

        int ans = Prime();

        if(ans == -)

            cout << "?" << endl;

        else

            cout << ans << endl;

    }

    return ;

}