N = int(input())
v = list(map(int, input().split()))

v.sort()
ans = None

a = None
b = None

for i in range(N-1):
    mi = 10000
    for j in range(len(v)-1):
        for k in range(j+1,len(v)):
            if mi >= abs(v[j]-v[k]):
                mi = abs(v[j]-v[k])
                a = j
                b = k
    
    ans = (v[a]+v[b])/2


    del v[a]
    del v[b-1]

    v.append(ans)


    v.sort()

print(ans)


