hdu2122

#include<stdlib.h>
#include<string.h>
#include<stdio.h>
#include<math.h>
#include<queue>
#define MAXN 1005

using namespace std;

int root[MAXN];

struct edge{
    int head;
    int tail;
    int cost;
    friend bool operator< (const edge &e1,const edge &e2){
        return e1.cost > e2.cost;
    }
};
priority_queue<edge> qn;

int findroot(int index){
    if(root[index] == -1)
        return index;
    else
        return root[index] = findroot(root[index]);
}
int kruskal(){
    int count;
    edge ebuf;
    count=0;
    while(!qn.empty()){
        ebuf = qn.top();
        qn.pop();
        int bufroot1 = findroot(ebuf.head);
        int bufroot2 = findroot(ebuf.tail);
        if(bufroot1 != bufroot2){
            root[bufroot1] = bufroot2;
            count+=ebuf.cost;
        }
    }
    return count;
}
int main(){
    int i;
    int n;
    int m;
    int u,v,cost,complete;
    edge edgebuf;
    
    freopen("in.txt","r",stdin);
    freopen("out.txt","w",stdout);

    while(scanf("%d",&n)!=EOF){    
        for(i=0;i<n;i++){
            root[i]=-1;
        }
        scanf("%d",&m);
        for(i=0;i<m;i++){
            scanf("%d %d %d",&u,&v,&cost);
            edgebuf.head = u;
            edgebuf.tail = v;
            edgebuf.cost = cost;
            qn.push(edgebuf);
        }
        int costbuf = kruskal();
        int count;
        count=0;
        for(i=0;i<n;i++){
            if(root[i] == -1)
                count++;
        }
        if(count == 1)
            printf("%d\n\n",costbuf);
        else
            printf("impossible\n\n");
    }
    return 0;
}