program aa;
var
  maxa,maxb,suma,sumb:longint;
function min(a,b:longint):longint;
begin
  if a>b then exit(b)else exit(a);
end;
function fct:longint;
begin
  maxa:=min(maxa,suma);
  maxb:=min(maxb,sumb);
  if maxa=0 then exit(maxb);
  if maxb=0 then exit(maxa);
  if (suma+sumb)div(sumb+1)>maxa then exit((sumb+1)*maxa+sumb);
  if (suma+sumb)div(suma+1)>maxb then exit((suma+1)*maxb+suma);
  exit(suma+sumb);
end;
begin  
  while not eof do
    begin  
      readln(suma,sumb,maxa,maxb);
      writeln(fct);
    end;
end.