There is a polyline going through points (0, 0) – (*x*, *x*) – (2*x*, 0) – (3*x*, *x*) – (4*x*, 0) – ... - (2*kx*, 0) – (2*kx* + *x*, *x*) – .... 

We know that the polyline passes through the point (*a*, *b*). Find minimum positive value *x* such that it is true or determine that there is no such *x*.
Only one line containing two positive integers *a* and *b* (1 ≤ *a*, *b* ≤ 10<sup class="upper-index">9</sup>).
def run1(x, y):
    if x < y:
        return -1;
    cst = (x - y) * 0.5;
    l = 1; r = 1000000001;
    ans = - 1.0;
    while(l <= r):
        m = (l + r) >> 1;
        now = cst / m;
        if now >= y:
            ans = now;
            l = m + 1;
        else:
            r = m - 1;
    return ans;

def run2(x, y):
    cst = (x + y) * 0.5;
    l = 1; r = 1000000001;
    ans = - 1.0;
    while(l <= r):
        m = (l + r) >> 1;
        now = cst / m;
        if( now >= y ):
            ans = now;
            l = m + 1;
        else:
             r = m - 1;
    return ans;

x, y = map(int, input().split());
p = run1(x, y);
q = run2(x, y);

ans = - 1.0;

if(ans < 0 or (p > 0 and p < ans) ):
    ans = p;
if(ans < 0 or (q > 0 and q < ans) ):
    ans = q;
print (ans)


