How to sum two rows at a time in matrix

I have a matrix of size 6 by 3

A = [1 2 3; 3 4 5; 4 5 6; 5 4 3; 3 4 3; 3 2 1]

I want to make sum of two rows at a time, so as to get result

[18; 27; 16]

Answer 1

[Adam]

sum( reshape( A', 6, 3 ) )