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 = 50
a, b = map(int, input().split())
c, d = map(int, input().split())

le = Decimal(0)
rg = Decimal(10 ** 10)

gr = a * d > b * c

for i in range(200):
    mid = (le + rg) / Decimal(2)

    val = 0
    if gr:
        val = (a - mid) * (d - mid) - (b + mid) * (c + mid)
    else:
        val = (a + mid) * (d + mid) - (b - mid) * (c - mid)

    now_gr = val > 0

    if gr == now_gr:
        le = mid
    else:
        rg = mid

print('%.15f' % ((le + rg) / 2))
