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*.
from decimal import *
getcontext().prec = 100
a, b, c, d = [Decimal(i) for i in input().split()]
l = Decimal(0)
r = Decimal(10 ** 9 + 1)
while r - l > Decimal('0.00000000001'):
    m = (l + r) / 2
    xm = a - m
    xM = a + m
    ym = b - m
    yM = b + m
    zm = c - m
    zM = c + m
    wm = d - m
    wM = d + m
    exxw = [xm * wm, xm * wM, xM * wm, xM * wM]
    exyz = [ym * zm, ym * zM, yM * zm, yM * zM]
    if xm < 0 < xM or wm < 0 < wM:
        exxw.append(Decimal(0))
    if ym < 0 < yM or zm < 0 < zM:
        exyz.append(Decimal(0))
    ispos = False
    isneg = False
    for xw in exxw:
        for yz in exyz:
            if xw - yz < 0:
                isneg = True
            if xw - yz > 0:
                ispos = True
    if isneg and ispos:
        r = m
    else:
        l = m
print(round((l + r) / 2, 12))