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())
l = 0
r = 10 ** 9 + 1
if (a * d == b * c):
    print(0)
else:
    for i in range(10000):
        x = (l + r) / 2
        a1 = (a - x) * (d - x)
        a2 = (a + x) * (d + x)
        b1 = (b - x) * (c - x)
        b2 = (b + x) * (c + x)
        mna = min(a1, a2)
        mxa = max(a1, a2)
        mnb = min(b1, b2)
        mxb = max(b1, b2)
        if (mxa >= mnb and mxb >= mna):
            r = x
        else:
            l = x
    print(x)