/* Compute mean of numbers from stdin */
/* Written by Fred Smith, July 1990*/
#include <stdio.h>

int main(void)
{
    double value, sum=0.0;
    int count=0;

    while (scanf("%lf", &value) == 1) {
        ++count;
        sum += value;
    }
    printf("%.2f", sum/count);
    return 0;
}