#include <cstdio>
using namespace std;

int x[200],y[200],way[200]={0},map[200][200]={{0}};
double dis[200][200]={{0}};
bool head[200]={false};

int main(void)
{
	freopen("firez.in","r",stdin);
	freopen("firez.out","w",stdout);
	int i,n;
	double temp;
	double ave=0;
	scanf("%d\n",&n);
	for (i=0;i<n;i++)
	{
		scanf("%d %d %d %d %lf\n",&x[i],&y[i],&x[i+1],&y[i+1],&temp);
		ave+=temp;
	}
	ave/=(n/2+1);
	printf("%.4lf\n",ave);
	fclose(stdin);
	fclose(stdout);
	return(0);
}