# 差が小さければ嬉しい
n = int(input())
arr = sorted(list(map(int, input().split())))

while len(arr) > 1:
  d = [0 for _ in range(len(arr)-1)]
  for i in range(len(arr)-1):
    d[i] = [i, arr[i+1] - arr[i]]
  d = list(sorted(d, key = lambda x : x[1]))
  i = d[0][0]
  x = (arr[i] + arr[i+1])/2.0
  arr = arr[:i] + arr[i+2:]
  arr.append(x)
  arr = list(sorted(arr))

print(arr[0])