class Solve:
    def __init__(self):
        self.N = int(input())
        self.L = [int(i) for i in input().split()]
        self.K = int(input())

        self.l, self.r = max([l/self.K for l in self.L]), min(max(self.L)+1, sum(self.L)/self.K+1)

    def check(self, l):
        k = 0
        L = [s for s in self.L if s >= l]
        while True:
            k += L.pop() // l + len(L)
            L = [s - l for s in L if s >= l*2]
            if k >= self.K:
                return True
            elif not L:
                return False

    def solve(self):
        while self.r - self.l > 10**-9:
            m = (self.l + self.r) / 2
            if self.check(m):
                self.l = m
            else:
                self.r = m
        return self.l

print(Solve().solve())