#include<stdio.h>
#include<algorithm>
using namespace std;
int set[1100];
struct record
{
	int beg;
	int end;
	int money;
}s[11000];
int find(int fa)
{
	int ch=fa;
	int t;
	while(fa!=set[fa])
	fa=set[fa];
	while(ch!=fa)
	{
		t=set[ch];
		set[ch]=fa;
		ch=t;
	}
	return fa;
}
void mix(int x,int y)
{
	int fx,fy;
	fx=find(x);
	fy=find(y);
	if(fx!=fy)
	set[fx]=fy;
}
bool cmp(record a,record b)
{
	return a.money<b.money;
}
int main()
{
	int n,m,j,i,sum,village,road;
	while(scanf("%d%d",&village,&road)!=EOF)
	{
		
		for(i=0;i<village;i++)
		set[i]=i;
		for(i=0;i<road;i++)
		{
			scanf("%d%d%d",&s[i].beg,&s[i].end,&s[i].money);
		}
		sort(s,s+road,cmp);
		sum=0;
		for(i=0;i<road;i++)
		{
		    if(find(s[i].beg)!=find(s[i].end))
		    {
		    	mix(s[i].beg,s[i].end);
		    	sum+=s[i].money;
		    }
		}
		m=0;
		for(i=0;i<village;i++)
		{
			if(set[i]==i)
			m++;
		}
		if(m>1)
		printf("impossible\n\n");
		else
		printf("%d\n\n",sum);
	}
	return 0;
}