#include <stdio.h>
#include <stdlib.h>

#define NMAX 100000000

int main()
{
	int x = 0, n = 0;
	unsigned long long somme = 0;
	float moy = .0;

	scanf("%d", &x);
	while(x >= 0)
	{
		somme += x;
		n++;
		scanf("%d", &x);
	}
	int length = n;
	moy = (float)somme / length;
	printf("%.2f\n", moy);

	return 0;
} // main()