import sys
input = lambda :sys.stdin.readline()[:-1]
ni = lambda :int(input())
na = lambda :list(map(int,input().split()))
yes = lambda :print("yes");Yes = lambda :print("Yes");YES = lambda : print("YES")
no = lambda :print("no");No = lambda :print("No");NO = lambda : print("NO")
#######################################################################


X = 10 ** 3
X4 = X ** 4

c = ni()
cc = X ** 5 * c
ok = 0
ng = 10 ** 100


while abs(ok - ng) > 1:
    x = ok + ng >> 1

    if x ** 5 + X4 * x <= cc:
        ok = x
    else:
        ng = x
p, q = divmod(ok, X)
# print(ok)
print(str(p) + "." + "0" * (3 - len(str(q))) + str(q))