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*.
# your code goes here

e=input().split()
q=input().split()

a=int(e[0])
b=int(q[1])



c=int(e[1])
d=int(q[0])

s=abs(a*b-c*d)

p=[]

m=abs(s/(c+d+a+b))

p.append(m)

p.append(abs(s/(c+d+a-b)))



m=abs(s/(c+d-a+b))
p.append(m)


n=abs(s/(c+d-a-b))

p.append(n)


p.append(abs(s/(c-d+a+b)))

p.append(abs(s/(c-d+a-b)))
p.append(abs(s/(c-d-a+b)))
p.append(abs(s/(c-d-a-b)))

p.append(abs(s/(-c+d+a+b)))
p.append(abs(s/(-c+d+a-b)))
p.append(abs(s/(-c+d-a+b)))
p.append(abs(s/(-c+d-a-b)))

p.append(abs(s/(-c-d+a+b)))
p.append(abs(s/(-c-d+a-b)))
p.append(abs(s/(-c-d-a+b)))
p.append(abs(s/(-c-d-a-b)))



print(min(p))
