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

main(int argc, char **argv)
{
  int i;
  double total, n, x;

  total = 0;
  n = 0;

  if (argc == 1) {
    fprintf(stderr, "usage: stde numbers...\n");
    exit(1);
  }

  for (i = 1; i < argc; i++) {
    if (sscanf(argv[i], "%lf", &x) == 1) {
      total += x;
      n++;
    } else {
     fprintf(stderr, "Argument %s not a number\n", argv[i]);
     exit(1);
    }
  }
  printf("%.3lf\n", total/n);
  return 0;
}