# n=5
# k=10000
# # l=[99, 88, 77, 66, 55]
# l=[99, 88, 77, 66, 55]

n=int(raw_input())
l=map(int,raw_input().split())
k=int(raw_input())

def C(x):
    num=0
    for i in xrange(n):
        num+= int(l[i]/x)
    return num >= k

lb = 0
ub = 10000

for i in xrange(100):
    mid = float(lb+ub)/2
    if C(mid):lb=mid
    else:ub=mid

print float(ub)*100/100