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

lo = 0
hi = 10 ** 9

while abs(lo - hi) > 10 ** (-10):
    mid = (lo + hi) / 2

    a1 = a - mid
    a2 = a + mid
    b1 = b - mid
    b2 = b + mid
    c1 = c - mid
    c2 = c + mid
    d1 = d - mid
    d2 = d + mid

    l = False
    h = False
    
    for i in [a1*d1, a1*d2, a2*d1, a2*d2]:
        for j in [b1*c1, b1*c2, b2*c1, b2*c2]:
            if i - j <= 0:
                l = True
            if i - j >= 0:
                h = True

    if l and h:
        hi = mid

    else:
        lo = mid

print(lo)