Fred has a rocket! He wants the rocket to fly high, but doesn't the rocket to consume too much fuel. Knowing the various relevant concepts in physics, chemistry, and *biology*, he has deduced that the maximum height of the rocket is the result of a cubic polynomial , where is the fuel setting on the rocket booster. Furthermore, you can assume that , as a higher rocket booster setting always corresponds to higher height. Of course, a higher rocket booster setting will result in more fuel being consumed, so Bob wants you to find the minimum booster setting (value of ) such that the maximum height (value of ) is at least . Do note that must be nonnegative.

**For this problem, using double precision float pointing numbers (double in java and c++) is recommended**

#### Constraints

#### Input Specification

The first line contains 4 decimal values, corresponding to , , , and , respectively.

#### Output Specification

One line with one decimal value, the minimum value of such that . Your answer will be regarded as correct if its absolute value from the accepted answer is less than or equal to

#### Sample Input

`1 2 3 6`

#### Sample Output

`1.0`

#### Sample Explanation

is the minimum value such that

## Comments