bai tap pascal so 28 day pa` con

PROGRAM SONGUOC;
USES CRT;
VAR a: integer;
n: string;
BEGIN
CLRSCR;
WRITE('Nhap vao 1 so co 4 chu so');
READLN(n);
FOR a:=4 DOWNTO 1 DO WRITE(n[a]);
READLN;
END.