#include<stdio.h>
int n,m;
float sum=0,degree[255];
int main()
{
	freopen("tunel.in","r",stdin);
	freopen("tunel.out","w",stdout);
	scanf("%d %d",&n,&m);
	int i,a,b,c;
	for(i=1;i<=m;i++)
	{
		scanf("%d %d %d",&a,&b,&c);
		degree[a]++;
		degree[b]++;
		sum=sum+c;
	}
	float val=0;
	for(i=1;i<=n;i++)
		val=val+1/(degree[i]);
	printf("%f",sum*val);
	return 0;
}