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*.
def seg(x, y, h):
    A = [x - h, x + h]
    B = [y - h, y + h]
    Z = []
    for a in A:
        for b in B:
            Z.append(a * b)
    Z.sort()
    return (Z[0], Z[-1])

def check(a, b, c, d, h):
    x1, y1 = seg(a, d, h)
    x2, y2 = seg(b, c, h)
    return max(x1, x2) <= min(y1, y2)

a, b = map(int, input().split())
c, d = map(int, input().split())
l = 0
r = max(abs(a), abs(b), abs(c), abs(d))
for i in range(100):
    m = (l + r) / 2
    if check(a, b, c, d, m):
        r = m
    else:
        l = m
print((r + l) / 2)

