#include<stdio.h>
#include<algorithm>
using namespace std;
struct st
{
	int s,e,dis;
}edge[200010];
bool cmp(const st&a,const st&b)
{
	return a.dis>b.dis;
}
int flag = 0;
int Kruskal(int v,int e)
{
	int i,j,an1,an2,sum = 0;
	int count = 1;
	int set[100001];
	for(i = 1;i <= v;i++)
		set[i] = i;
	sort(edge + 1,edge + e + 1,cmp);
	i = 1;
	while(count < v)
	{
		an1 = set[edge[i].s];
		an2 = set[edge[i].e];
		if(an1 != an2)
		{
			count++;
			if(edge[i].dis == -1)
			{
				flag = 1;
				break;
			}
			else
		    	sum += edge[i].dis;
			for(j = 1;j <= v;j++)
				if(set[j]==an2)
					set[j] = an1;
		}
	//	printf("%d\n",sum);
		i++;
	}
	return sum;
}
int main()
{
	int i,j,n,m,k,sum;
	while(scanf("%d%d",&n,&m)!=EOF)
	{
	k = 0;
	for(i = 1;i <= n;i++)
		for(j = 1;j <= n;j++)
		{
			edge[++k].s = i;
			edge[k].e = j;
			edge[k].dis = -1;
		}
	for(i = 1;i <= m;i++)
	{
		scanf("%d%d%d",&edge[i].s,&edge[i].e,&edge[i].dis);
	}
	sum = Kruskal(n,m);
	if(flag)
		printf("-1\n");
	else
    	printf("%d\n",sum);
	}
	return 0;
}
/*Sample Input

5 8
1 2 3
1 3 7
2 3 10
2 4 4
2 5 8
3 4 6
3 5 2
4 5 17
Sample Output

42
*/