数字反转 求哪里错了

program  ex1_1;
  var a,b,c,n:longint;
  begin
     readln(n);
     a:=n mod 10;
     b:=n div 10 mod 10;
     c:=n div 100;
     n:=a*100+b*10+c;
     writeln(n);

readln； end.