M and N are integers satisfying 0 < N < M and A denotes the point (M,N)

Point B denotes the reflection of point A across the line y=x
Point C denotes the reflection of point B across the y-axis
Point D denotes the reflection of point C across the x-axis
Point E denotes the reflection of point D across the line y-axis

Find M+N, given that the area of the pentagon ABCDE is 451.