VAR i,p1,d,min,s1,s2,k:int64;
Begin
Readln(p1,d,min,s1);
while (s2 + p1 <= s1) do
Begin
s2:=s2 + p1;
if p1 - d >= min then p1:=p1 - d else p1:=min;
k:=k + 1;
end;
//Writeln(k);
//if (s2 < s1) and (p1 <= min) then k:=k + ((s1 - s2) div p1);
if k <> 0 then Writeln(k) else Writeln(0);
Readln;
END.