int S(void)
{
  int n;
  if(lookahead == 'a') {
    match('a');
    n = S();
    match('a');
    return n;
  }
  else if(lookahead == 'b') {
    int n;
    match('b')'
    n = S();
    match('b');
    return n;
  }
  else {
    n = L();
    return n;
  }
}


int L(void)
{
  int n;

  if(lookahead == 'c') {
    match('c');
    n = L();
    return n + 1;
  }
  else {
    return 0;
  }
}