who know please tell me ?
give me a sample programme is the best!

var
  a:array[1..1000]of longint;
n,i,j:longint;

function nod(k,l:longint):longint;
begin
repeat
if k<l then l:=l mod k else k:=k mod l;
until (k=0)or(l=0);
nod:=k+l;
end;
begin
read(n);
for i:=1 to n do
read(a[i]);
for i:=n-1 downto 1 do
a[i]:=nod(a[i],a[i+1]);
write(a[1]);
end.