if __name__ == "__main__":
x = float(input())
l = -10000 # 避免 x 出现值为 [0, 1]
r = 10000
while r - l > 1e-8:
mid = (l + r) / 2
if (pow(mid, 3) >= x):
r = mid
else:
l = mid
print("%.6f" %(l))