c = int(input())
# x=v/10^3
l = 0
r = 4000
while r - l > 1:
    mid = (l + r) // 2
    if mid ** 5 + mid * 10 ** 12 <= c * 10 ** 15:
        l = mid
    else:
        r = mid
print(f'{l // 1000}.{l % 1000:03d}')