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

   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
         if ((nok = 1) or (nok = 2) or (nok = nor * 2)) then
         writeln((nor * 3) - 2)
         else begin
         cht:= (nok - 1) div 2 + 1;
         cht2:= 3*(nor - cht)*((nor - cht)+1)/2 - (nor - cht)*3 + (nor - cht)*2;
         cht1:= 3*(cht-1)*((cht-1)+1)/2 - (cht-1)*3 + (cht-1)*2;

         if (nor <> n) then
            cht:=(n - nor) * 3 - n * 3 + n * 2 - 2
         else
            cht:=n * 2 - 2;
            writeln((ob - cht - cht1 - cht2 - 1):0:0);
         end
   end;
   readln;
end.