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 = self.L[0]/self.K, max(self.L)+1

    def check(self, l):
        idx = 0
        s = self.L[idx]
        for i in range(self.K):
            if(s >= l):
                s -= l
            else:
                while(s < l):
                    idx += 1
                    try:
                        s = self.L[idx]
                    except IndexError:
                        return False
                s -= l
        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())