Complete reaction of acetaldehyde with excess formaldehyde, upon heating with conc. \( \text{NaOH} \) solution, gives P and Q. Compound P does not give Tollens’ test, whereas Q on acidification gives positive Tollens’ test. Treatment of P with excess cyclohexanone in the presence of catalytic amount of p-toluenesulfonic acid (PTSA) gives product R.
Sum of the number of methylene groups (\( -\text{CH}_2- \)) and oxygen atoms in R is ______.
