program p1121;
type
    ORD=record
        x,y:integer;
        end;
var
    s,e,ma:ORD;
    p:integer;

function move(s:ORD; op:integer):ORD;
begin
    case op of
    1:begin inc(s.x); end;
    2:begin inc(s.y); end;
    end;
    exit(s);
end;

procedure search(s:ORD);
var
    op:integer;
    t:ORD;
begin
    if s=e then begin
        inc(p);
        exit;
    end;
    for op:=1 to 2 do begin
        t:=move(s,op);
        if ((t.x in [1..e.x]) and (t.y in [1..e.y])) then
            search(t);
    end;
end;


begin
    readln(e.x,e.y,ma.x,ma.y);
    s.x:=0; s.y:=0;
    p:=0;
    search(s);
    writeln(p);
end.