assert(k > 1);
int outer = k, A_cols = k / 2;
read_mat(outer, A_cols, &A);
read_mat(A_cols, outer, &B);
while (!done(A, B)) {
    read_row(&A);
    read_col(&B);
    outer++;
}
gemm_skinny(A, B, &C, outer, A_cols, outer);