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())

a *= int(1e9)
b *= int(1e9)
c *= int(1e9)
d *= int(1e9)

def jg(e):
    if(a * d < b * c):
        # print((a + e) * (d + e) , " , " , (b - e) * (c - e));
        if((a + e) * (d + e) >= (b - e) * (c - e)): return True
        else: return False
    else:
        # print((a - e) , " , " , (d - e) , " , " , (b + e) , " , " , (c + e))
        if((a - e) * (d - e) <= (b + e) * (c + e)): return True
        else: return False
def f():
    one = 1
    l = 0
    r = int(1e18) + one
    while(r - l - one > one):
        # print(a , b , c , d)
        c = l + round((r - l - one) / 2) + one
        if(jg(c) == True): r = c
        else: l = c - one
    if(r - l - one < one): return l
    if(r - l - one == one):
        if(jg(r - one) == True): return r - one
        else: return r

print(f() / 1e9);