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):
        idx, s, k = 0, 0, 0
        S = sum(self.L)
        while(k < self.K):
            if(S < l*(self.K-k)):
                return False
            while(s < l):
                try:
                    s = self.L[idx]
                    S -= s
                except IndexError:
                    return False
                idx += 1
            dk = s // l
            s -= l * dk
            k += dk
        return True

    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())