Three poles stand evenly spaced along a line. Their heights are a, b and c meters, from left to right. We will call the arrangement of the poles _beautiful_ if the tops of the poles lie on the same line, that is, b-a = c-b.  Determine whether the arrangement of the poles is beautiful.
(lambda x: print('Yes') if x[1] - x[0] == x[2] - x[1]  else print('No'))(list(map(int,input().split())))
(lambda x: print('YES') if x[1] - x[0] == x[2] - x[1]  else print('NO'))(list(map(int,input().split())))