import sys
inputs = sys.stdin.readlines()

n = int(inputs[0])
v_list = list(map(int, inputs[1].split()))
v = sorted(v_list)

v_diff_list = [v[i+1] - v[i] for i in range(len(v)-1)]
for _ in range(len(v)-1):
    v_diff_list = [v[i+1] - v[i] for i in range(len(v)-1)]
    index = v_diff_list.index(min(v_diff_list))
    val = (v.pop(index) + v.pop(index)) / 2
    v.insert(index, val)
print(val)