{
  for (int c0 = 1; c0 <= min(M, N); c0 += 1) {
    S1(c0);
    for (int c1 = 1; c1 <= M; c1 += 1)
      S2(c0, c1);
  }
  for (int c0 = M + 1; c0 <= N; c0 += 1)
    for (int c1 = 1; c1 <= M; c1 += 1)
      S2(c0, c1);
  for (int c0 = N + 1; c0 <= M; c0 += 1)
    S1(c0);
}