程序超时，怎么改

var
a:array[1..1000]of char;
b:array[1..1000]of integer;
i,n,t:integer;
begin
 readln(n);
 i:=0;
 repeat
  i:=i+1;
  read(a[i]);
  until ord(a[i])=13;
 readln;
 for t:=1 to (i-1) do
  begin
  b[t]:=ord(a[t])+n;
  if b[t]>122 then b[t]:=b[t]-26;
  write(chr(b[t]));
  end;
 writeln;
end.