n = input()
nlist = []
for i in range(0,int(n)):
  x = input()
  nlist.append(float(x))
  
def avg(list):
    for i in range(0,int(n)-1):
        list.insert(0,float((list.pop(0) + list.pop(0)))/2)
    return list[0]    
        
print(avg(nlist))
