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>).
a= int(input('Enter first coefficient:'))
b= int(input('Enter second coefficient:'))
flag1= True
flag2= True
if a>=b:
if a==b:
A= float(b)
else:
t= float((a-b)/(2*b))
if(t<1):
flag1= False
A= float((a-b)/(2*t))
else:
flag1= False
t= float((a+b)/(2*b))
if(t<1):
flag2=False
t1= float((a+b)/(2*t))
if(flag1==False):
A= float(t1)
else:
A= float(min(A, t1))
if(flag1 and flag2):
print(A)
else:
print("-1")