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*.
if __name__ == '__main__':
    a, b = map(int, input().split())
    c, d = map(int, input().split())

    if a == 0 and b == 0 and c == 0 and d == 0:
        print(0)
        exit(0)

    l = a + c
    r = b + d
    s = l + r

    e = (a * s - (a + b) * l)
    f = (b * s - (a + b) * r)
    g = (c * s - (c + d) * l)
    h = (d * s - (c + d) * r)

    print(min(map(abs, (e, f, g, h))) / s)