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*.
from decimal import *

getcontext().prec = 50
a, b = map(int, input().split())
c, d = map(int, input().split())

answer = None

for k in range(1 << 4):
    le = Decimal(0)
    rg = Decimal(10 ** 11)

    def f(t):
        fi = a
        if k & 1:
            fi += t
        else:
            fi -= t

        fi *= (d + t if k & (1 << 1) else d - t)

        se = (b + t if k & (1 << 2) else b - t)
        se *= (c + t if k & (1 << 3) else c - t)

        return abs(fi - se)

    for i in range(200):
        m1 = le + (rg - le) / Decimal(3)
        m2 = rg - (rg - le) / Decimal(3)

        if f(m1) > f(m2):
            le = m1
        else:
            rg = m2

    if f(le) < 1e-8:
        if answer == None:
            answer = le
        else:
            answer = min(answer, le)

print(answer)
