#include <stdio.h>

int main()
{
	int tab[100] = {0};

	int x = 0, n = 0;
	scanf("%d", &x);
	while(x >= 0)
	{
		tab[n] = x;
		n++;
		scanf("%d", &x);
	}
	int length = n;

	int sum = 0;
	for(int i = 0; i < length; i++)
	{
		sum += tab[i];
	}

	float moy = (float)sum / length;
	printf("%.2f\n", moy);

	return 0;
} // main()