no_name_1.pas

program bt;
uses crt;
var inp: anstring;
    i: longint;
    tmp, chk: byte;
    tong: int64;
begin
 clrscr;
 write('Nhap n: ');
 readln(inp);
 for i:=1 to length(inp) do begin
  val(inp[i], tmp, chk);
  if i mod 2=0 then tong:=tong-tmp else tong:=tong+tmp;
 end;
 write(tong);
 readkey;
end.