Certain number of birds are sitting on two trees A and B. Birds sitting on tree A, tell to the birds sitting on tree B, that if 2 birds from tree B shift to the tree A, then we are equal in number. However, the birds sitting on tree B, tell those sitting on A, that if two birds from your side (tree A) shift to our side (tree B), then we become double than you (tree A). How many birds are sitting on the two trees A and B, respectively?