import java.util.Scanner;

public class Main
{
    private static int N=510;
    private static int n,m;
    private static int[][] g=new int[N][N];
    private static boolean[] st=new boolean[N];
    private static int[] dist=new int[N];
    private static int max=100000000;

    public static void main(String[] args)
    {
        Scanner scan=new Scanner(System.in);

        n=scan.nextInt();
        m=scan.nextInt();

        for(int i=1;i<=n;i++)
            for(int j=1;j<=n;j++)
            {
                if(i==j)
                    g[i][j]=0;
                else 
                    g[i][j]=max;
            }
        //初始化每个点到已选择点的集合的距离
        for(int i=1;i<=n;i++)
            dist[i]=max;

        for(int i=0;i<m;i++)
        {
            int a=scan.nextInt();
            int b=scan.nextInt();
            int c=scan.nextInt();
            g[a][b]=g[b][a]=Math.min(g[a][b], c);
        }

        int t=prim();
        if(t==max)
            System.out.println("impossible");
        else 
            System.out.println(t);

        scan.close();

    }

    private static int prim()
    {
        int res=0;
        for(int i=0;i<n;i++)
        {
            int t=-1;
            for(int j=1;j<=n;j++)
            {
                if(!st[j]&&(t==-1||dist[t]>dist[j]))
                    t=j;
            }

            if(i!=0&&dist[t]==max) return max;
            if(i!=0)
                res+=dist[t];

            for(int j=1;j<=n;j++)
                dist[j]=Math.min(dist[j], g[t][j]);

            st[t]=true;

        }
        return res;
    }

}