for (int c1 = 1; c1 <= 10; c1 += 1) {
  for (int c3 = 1; c3 <= c1; c3 += 1)
    S1(c1, c3);
  for (int c3 = 11; c3 <= M; c3 += 1)
    S2(c1, c3);
}