program hehe;
var
 c,p,v1,v0,a,yidu,n,shiji:integer;
procedure init;
begin
 assign(input,'MrBA.in');assign(output,'MrBA.out');
 reset(input);rewrite(output);
end;
begin
 init;
 read(c,v0,v1,a,p);
 yidu:=v0+a;
 shiji:=v0;
 n:=2;
  if v0>=c then write(1)
           else begin
  while shiji<=c do
   begin
   if yidu+p<v1  then  yidu:=a+yidu
       else    yidu:=v1-p;
     
       shiji:=yidu+shiji;
       inc(n);
   end;
                end;
 if v0<c then write(n);
 close(input);
 close(output);
end.