#include <stdio.h>
#include <stdlib.h>
int main (int argc, char *argv[])
{ int sum, count, n;
  count = 0;
  sum = 0;
  while (1 == scanf("%d", &n))
   { sum = sum + n;
     count++;
   }
  printf("%f\n", (float)sum / (float)count);
  exit(0);
}