N=int(input())
vn=[int(k) for k in input().split()]

def sort(vn):
    for i in range(0,len(vn)-1):
        select_min(vn,i)

def select_min(vn,i):
    min=i
    for j in range(i+1,len(vn)):
        if vn[min]>vn[j]:
            min=j
    vn[i],vn[min]=vn[min],vn[i]

sort(vn)
for l in range(0,len(vn),2):
    vn.insert(l+2,(vn[l]+vn[l+1])/2)
    
if N<=3:   
    print(vn[-1])
else:
    print((vn[-1]+vn[-2])/2)