import itertools

def calc(vlist):
    sum = vlist[0]
    for i in range(len(vlist) - 1):
        sum = ((sum + vlist[i+1]) / 2)        

    return sum

try:
    n = int(input())
    
    v = [int(x) for x in input().split(' ')]
    
    pattern = itertools.permutations(v)
    
    results = []
    for plist in pattern:
      results.append(calc(plist))
      
    print(max(results))
    
except ValueError:
    print("数値を入力してください")