function Del(s:string):string;
var i,j:byte;
begin
i:=1;
while i<=length(s)do
begin
k:=0;
for j:=length(s) downto i+1 do
if s[j]=s[i] then
begin
k:=1;
delete(s,j,1);
end;
if k=1 then delete(s,i,1)
else inc(i);
end;
Del:=s;
end;