var
   n, nap, nor, nok, ob, cht, cht1, cht2: int64;
begin
   readln(n, nap, nor, nok);
   ob:=3 * n * (n + 1) div 2 - n;

   if (nap = 0) then begin
         if ((nok = 1) or (nok = nor)) then
         writeln(nor * 3 - 1)
         else
         writeln('0');
   end;

   if (nap = 1) then begin
         cht := (nok - 1) div 2 + 1;
         cht2 := 3 *(nor - cht) * (nor - cht + 1) div 2 - (nor - cht);
         cht1 := 3 * (cht - 1) * cht div 2 - (cht - 1);
            writeln(ob - cht - cht1 - cht2 - 1);
         end;
   readln;
end.