How do I sum the elements of each corner of a matrix?

If I have a 4x4 matrix, how do i sum 4 elements in 4 corner of that matrix

for example my matrix will be : A=[1 2 3 4; 5 6 7 8 9;10 11 12 13; 14 15 16 17]

Thanks you so much

[Walter Roberson]

When you index with a list of values then what is selected is all the locations that meet all of the criteria. For example A([1 3],[2 4]) choses all the locations that are in row 1 or 3 and that are in columns 2 or 4. That would be a total of 4 locations.

Answer 1

[KSSV]

iwant = A(1,1)+A(1,end)+A(end,1)+A(end,end)