var t,z,k:byte; a,b:1..100;
  s:longint;
begin
read(t,z,a,b);
if (b>a) then begin
k:=b-a; s:=2*k*z+((k-1)*t);  end;
if(a>b) then begin k:=a-b; s:=(((2*k)+1)*z+(k+1)*t-1);   end;
write(s);end.