The determinant of a matrix 2 × 2 is defined as follows:

A matrix is called degenerate if its determinant is equal to zero. 

The norm ||*A*|| of a matrix *A* is defined as a maximum of absolute values of its elements.

You are given a matrix <img align="middle" class="tex-formula" src="https://espresso.codeforces.com/e78540a0de68f85833f82714a7141114b781276e.png" style="max-width: 100.0%;max-height: 100.0%;"/>. Consider any degenerate matrix *B* such that norm ||*A* - *B*|| is minimum possible. Determine ||*A* - *B*||.
The first line contains two integers *a* and *b* (|*a*|, |*b*| ≤ 10<sup class="upper-index">9</sup>), the elements of the first row of matrix *A*. 

The second line contains two integers *c* and *d* (|*c*|, |*d*| ≤ 10<sup class="upper-index">9</sup>) the elements of the second row of matrix *A*.
a, b= map(int, input().split())
c, d = map(int, input().split())
if a * d - b * c == 0:
    print(0)
else:
    curpos = a * d - b * c >= 0
    small = 0;
    large = 1e18
    for iteration in range(200):
        avg = (small + large) / 2
        works = False
        for ach in range(-1, 2, 2):
            for bch in range(-1, 2, 2):
                for cch in range(-1, 2, 2):
                    for dch in range(-1, 2, 2):
                        newpos = (a + ach * avg) * (d + dch * avg) - (b + bch * avg) * (c + cch * avg) >= 0
                        if newpos != curpos:
                            works = True
        if works:
            large = avg
        else:
            small = avg
    print(small)
