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*.
glist = []
def recurse(level, li):
  if ( level == 0):
    glist.append( li[0] + li[1] - li[2] - li[3])
    glist.append( li[0] + li[1] - li[2] + li[3])
    return
  else :
    li2 = li[:]
    li2[level] = (-1)*li2[level]
    ret1 = recurse(level-1 , li)
    ret2 = recurse(level-1 , li2)
    return
a , b  = map(int, input().split());
c , d = map(int , input().split());
det = b*c - a*d ;
li = [a,d,c,b];
recurse(3,li)

phi =1000000000000;
for x in glist:
  if ( x != 0):
    if ( abs(det/x) < phi ):
      phi = abs(det/x)

print(phi)

