4

def sol(dep, n):
    commission = 0
    for i in range(n - 1):

        first_min = min(dep)
        dep.remove(first_min)

        second_min = min(dep)
        dep.remove(second_min)

        new_dep = first_min + second_min
        commission += new_dep * 0.05

        dep.append(new_dep)

    return commission


n = int(input())
deposit = [int(i) for i in input().split()]
print(sol(deposit, n))