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

v.sort()
ans = None

V = []
a = None
b = None
for i in range(1, N):
    V.append(abs(v[i]-v[i-1]))

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


    del v[a]
    del v[a]

    v.append(ans)


    v.sort()

print(ans)


