Plz help me, or give some test.

var
  st:array[1..1000] of integer;
  b,e,i,j,k,m,max,n,ist:integer;
  a:array[1..1000] of char;
  ch:char;

procedure readdata;
begin
  n:=0;
  while not eof do
  begin
    inc(n);
    read(ch);
    a[n]:=ch;
  end;
end;

procedure writedata;
begin
  for i:=b to e-1 do
  write(a[i]); writeln(a[e]);
end;

procedure push(x:integer);
begin
  st[ist]:=x;
  inc(ist);
end;

procedure pop(var x:integer);
begin
  dec(ist);
  x:=st[ist];
  st[ist]:=0;
end;

begin
  readdata;
  max:=0; ist:=1;
  for i:=1 to n-1 do
  begin
    j:=i;
    if (ist>=2) and (a[j]=a[st[ist-1]]) then
    begin
      k:=0; m:=ist-1;
      while (j<=n) and (m>=1) and (a[j]=a[st[m]]) do
      begin
        inc(j);
        dec(m);
        inc(k);
      end;
      k:=k*2;
      if k>max then
      begin
        max:=k;
        b:=m+1;
        e:=j-1;
      end;
      push(i);
    end                    else

    if (ist>=2) and (a[j+1]=a[st[ist-1]]) then
    begin
      inc(j);
      k:=0; m:=ist-1;
      while (j<=n) and (m>=1) and (a[j]=a[st[m]]) do
      begin
        inc(j);
        dec(m);
        inc(k);
      end;
      k:=k*2+1;
      if k>max then
      begin
        max:=k;
        b:=m+1;
        e:=j-1;
      end;
      push(i);
    end          else push(i);

  end;
  writedata;
end.

example:
Input:
1
output
_
Input:
22
output
_
Input
111232
output
232

It is necessary to remove the most left
It is 111