用free pascal编写程序,要具体（用while语句）

program Pi;
const d=0.0006; // 要提高精度, d 要减小.
var sum: double;
n, sign: longint;
begin
sign:=1;
sum:=0;
n:=1;
while (1/n>d) do
begin
sum:=sum+sign/n;
sign:=sign*(-1);
n:=n+2;
end;
writeln('Pi=', sum*4:10:7);
readln;
end.