Help me in solving LB01C problem

help
,
1

My issue

give submit button

My code

#Once the observations / logic is clear, click on 'Next' to continue.
A,C=map(int,input().split())
B=(A+C)//2
if((A+C)%2==0 and (A+C)%2!=0 ):
    print(B)
elif((A+C)%2!=0 ):
    print(-1)

Learning course: Python for problem solving - 1
Problem Link: CodeChef: Practical coding for everyone