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*.
# IAWT
m = list(map(int, input().split() + input().split()))

def f(r):
    a = (m[0] + r) * (m[3] + r)
    b = (m[0] + r) * (m[3] - r)
    c = (m[0] - r) * (m[3] + r)
    d = (m[0] - r) * (m[3] - r)
    x1 = min(a, b, c, d)
    x2 = max(a, b, c, d)
    
    a = (m[1] + r) * (m[2] + r)
    b = (m[1] + r) * (m[2] - r)
    c = (m[1] - r) * (m[2] + r)
    d = (m[1] - r) * (m[2] - r)
    y1 = min(a, b, c, d)
    y2 = max(a, b, c, d)
    if y1 > x2 or x1 > y2: return False
    return True


l = 0
r = 10 ** 20
for i in range(10000):
    mid = (l + r) / 2
    if f(mid):
        r = mid
    else:
        l = mid

print(l)
