An acid “A” which is an important constituent of vinegar; on reaction with Red P & Br2 gives a monobromoderivative (B) which on reaction with NH3 gives white solid (C). However ethanal on reaction with a mixture of ammonium chloride and sodium cyanide undergoes Strecker synthesis to give a product which on acidic hydrolysis gives another high melting solid (D). If x & y are the total no. of optical isomers of (C) & (D) respectively. while Z is the total number of dipeptides that (C) and (D) can form, then what is the value of x−3y+2z?