temp=input().split()

A=int(temp[0])

B=int(temp[1])



m=int((A+B)/2)



if m==(A+B)/2 and m>=0:

  print((int(m)))

else:

  print('IMPOSSIBLE')
import numpy as np



temp=list(map(int, input().split()))

temp=np.mean(temp)

if temp-int(temp)>0:

  output='IMPOSSIBLE'

else:

  output=int(temp)

  

print(output)
temp = input().split()
A = int(temp[0])
B = int(temp[1])
m = int((A + B) / 2)
if m == (A + B) / 2 and m >= 0:
    print((int(m)))
else:
    print("IMPOSSIBLE")

import numpy as np

temp = list(map(int, input().split()))
temp = np.mean(temp)
if temp - int(temp) > 0:
    output = "IMPOSSIBLE"
else:
    output = int(temp)
print(output)

-temp = input().split() -A = int(temp[0]) -B = int(temp[1]) -m = int((A + B) / 2) -if m == (A + B) / 2 and m >= 0: -    print((int(m))) +import numpy as np + +temp = list(map(int, input().split())) +temp = np.mean(temp) +if temp - int(temp) > 0: +    output = "IMPOSSIBLE" -    print("IMPOSSIBLE") +    output = int(temp) +print(output)