#include <bits/stdc++.h>
int main(void) {
  int N;
  int a[50];
  int length = sizeof(a) / sizeof(int);
  int step, i, j;
  for (step = length / 2; step > 0; step /= 2) {
    for (i = step; i < length; i++) {
      int tmp = a[i];
      int j = i;
      for (j = i; j >= step; j -= step) {
        if (a[j - step] > tmp) {
          a[j] = a[j - step];
        } else {
          break;
        }
      }
      a[j] = tmp;
    }
  }
  float sum = (a[0] + a[1]) / 2;
  if (N = 2) {
    printf("%f", sum);
  } else {
    for (int i = 2; i < N - 1; i++) {
      sum = (sum + a[i]) / 2;
    }
    printf("%f", sum);
  }
}
