Trace of Matrix

Chef is learning linear algebra. Recently, he learnt that for a square matrix $M$, $\mathop{\rm trace}(M)$ is defined as the sum of all elements on the main diagonal of $M$ (an element lies on the main diagonal if its row index and column index are equal). Now, Chef wants to solve some excercises related to this new quantity, so he wrote down a square matrix $A$ with size $N\times N$. A square *s