Sum each page of a 3D matrix and append sums as rows of new 2D matrix

I cannot for the life of me figure out why this for loop is overwriting the first row of my output variable (D). I have spent a few hours now reading through Matlab forums/documentation, and it appears that I've written this correctly but it's still overwriting.

I have a 2D matrix (A), a second 2D matrix (B), and I've concatenated these to make a 3D matrix (C) where Page 1 = A and Page 2 = B. I want to sum each page of C and name D such that each row of D is the sum of each column of each page in C. So, the final output for D should be [15 15 15; 25 25 25]. I believe the output is [0 0 0 ; 25 25 25] because Matlab is overwriting the first iteration of the for loop and pasting only the results of the second (and final) iteration.

Example code:

A = [5 5 5; 10 10 10]

B = [15 15 15; 10 10 10]

C = cat(3,A,B)

D = zeros(2,3)
for i = 2
    D(i,:) = sum(C(:,:,i),1)
end

Where am I going wrong?

Thank you in advance.

[May_the_degrees_of_freedom_be_with_you]

Finally solved it! Copying my answer here in case anyone else is having a similar problem.

Thank you to "M" from this thread (https://www.mathworks.com/matlabcentral/answers/376632-matrix-filling-with-for-loop)--I got this to work from trying an alternate form of the "i" parameter that "M" used.

A = [5 5 5; 10 10 10]

B = [15 15 15; 10 10 10]

C = cat(3,A,B)

D = zeros(2,3)
for i = 1:2
    D(i,:) = sum(C(:,:,i),1)
end

Answer 1

[Matt J]

D=permute(sum(C,1),[3,2,1])