【求助】帮忙看下代码

我是题意理解错了还是程序错了：

var s:array[2..20000]of boolean;n,i,j,x:integer;
begin
  read(n);fillchar(s,sizeof(s),true);
  write(3,' ');
  n:=n-3;x:=trunc(sqrt(n));
  for i:=2 to x do
    if s[i] then for j:=2 to x div i do s[i*j]:=false;
  for i:=2 to n do
    if s[i] and s[n-i] then break;
  if i>n-i then write(n-i,' ',i) else write(i,' ',n-i);
end.