/*
Simplification of dyn4.c, using the standard realloc() function.
*/

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

int doublearray_append(double **a,int *aspace,int *alen,double d)
{
  if (*alen == *aspace) {
    int yspace = *aspace * 2 + 1;
    double *y = (double *) realloc(*a,yspace * sizeof(double));
    if (!y) return 0;
    *a = y;
    *aspace = yspace;
  }
  (*a)[*alen] = d;
  ++*alen;
  return 1;
}

int main(void)
{
  double *x = 0;
  int xspace = 0;
  int xlen = 0;
  double d;
  int i;
  int j;

  while (scanf("%lf",&d) == 1)
    if (!doublearray_append(&x,&xspace,&xlen,d)) {
      printf("out of memory\n");
      exit(1);
    }

  while (xlen > 2) {
    j = 0;
    for (i = 1;i < xlen;++i)
      if (x[i] < x[j])
        j = i;
    x[j] = x[--xlen];
    j = 0;
    for (i = 1;i < xlen;++i)
      if (x[i] > x[j])
        j = i;
    x[j] = x[--xlen];
  }

  if (xlen == 1) printf("%f\n",x[0]);
  if (xlen == 2) printf("%f\n",(x[0] + x[1]) / 2);
  return 0;
}