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*.
import sys



input       = []
input_index = 0

def next(type, number = None):
	def next():
		global input, input_index
		
		
		while input_index == len(input):
			if sys.stdin:
				input       = sys.stdin.readline().split()
				input_index = 0
			else:
				raise Exception()
				
				
		input_index += 1
		
		return input[input_index - 1]
		
		
	if number is None:
		result = type(next())
	else:
		result = [type(next()) for _ in range(number)]
		
	return result
	
	
	
a, b, c, d = next(int, 4)
s = sum([a,b,c,d])
det = a*d-b*c

r1 = det / s

print(abs(r1))
