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*.
EPS = 1e-11
INF = float("inf")


def multiply ( a , b ):
    m = INF
    M = -INF
    for i in range(2):
        for j in range(2):
            m = min(m, a[i] * b[j])
            M = max(M, a[i] * b[j])

    return (m, M)

def intersect ( a , b ):
    return (a[0] <= b[1] and b[0] <= a[1])


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


lo = 0
hi = 1e9

nIters = 0
while nIters < 1000 and abs(lo - hi) > EPS:
    mi = (lo + hi) / 2

    i1 = multiply((a - mi, a + mi), (d - mi, d + mi))
    i2 = multiply((b - mi, b + mi), (c - mi, c + mi))

    if ( intersect(i1, i2) ):
        hi = mi
    else:
        lo = mi

    nIters += 1

print("{:.10f}".format(hi))
