var m,p,d,s,kq,sl:longint;
begin
    kq:=0;
    read(p,d,m,s);
    sl:=0;
    while sl<=s  do
    begin
        sl:=sl+p;
        if p-d>=m then p:=p-d
        else p:=m;
        inc(kq);
    end;
    write(kq-1);
end.