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

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

  while (scanf("%lf",&d) == 1) {
    if (xlen == xspace) {
      y = (double *) malloc((xspace * 2 + 1) * sizeof(double));
      if (!y) {
        printf("out of memory\n");
        exit(1);
      }
      if (x) {
        for (i = 0;i < xlen;++i)
          y[i] = x[i];
        free(x);
      }
      x = y;
      xspace = xspace * 2 + 1;
    }
    x[xlen++] = d;
  }

  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;
}