a, b = list(map(int, input().split()))



k = ( a + b )



if k%2 == 0:

  print((k//2))

else:

  print('IMPOSSIBLE')
a, b = list(map(int, input().split()))



if (a**2 - b**2) % (2 * (a - b)) == 0:

    print(((a**2 - b**2) // (2 * (a - b))))

else:

    print('IMPOSSIBLE')

a, b = list(map(int, input().split()))
k = a + b
if k % 2 == 0:
    print((k // 2))
else:
    print("IMPOSSIBLE")

a, b = list(map(int, input().split()))
if (a**2 - b**2) % (2 * (a - b)) == 0:
    print(((a**2 - b**2) // (2 * (a - b))))
else:
    print("IMPOSSIBLE")

-k = a + b -if k % 2 == 0: -    print((k // 2)) +if (a**2 - b**2) % (2 * (a - b)) == 0: +    print(((a**2 - b**2) // (2 * (a - b))))