题解 | #正则匹配#

for line in sys.stdin:
    n=float(line.strip())
    last=n
    new=last-((last**3-n)/(3*last**2))
    while abs(new-last)>0.000001:#精度要求
        last=new
        new=last-((last**3-n)/(3*last**2))
    print(format(new,'.1f'))