C=int(input())
left,right = 0, 10**17
while right-left > 1:
    mid = (right+left)//2
    if -(-mid**5//(10**12)) + mid <= C*10**3:
        left = mid
    else:
        right = mid
print(str(left//10**3)+"."+str(left//10**2%10)+str(left//10%10)+str(left%10))