import math
if __name__ == '__main__':
    n = int(input())
    Arrnums = sorted([float(x) for x in input().split(' ')])
    j = 0
    q = Arrnums[1]
    for i in range(j, n-1):
        q = (Arrnums[i] + q)/2
        j = i + 2
    print(q)