C=int(input())
result=0
for x in range(1,10000):
  y=x**5+x*10**12-C*10**15
  if y<=0:
    result=x
result=str(result)
if len(result)<4:
  result='0'*(4-len(result))+result
result=result[:-3]+'.'+result[-3:]
print(result)