This is my programme,please tell me why I got WA.Thank you!

var n,m,m0,ys:longint;
procedure pd(a,b:longint);
  var t:longint;
  begin
  if a<b then begin
                  t:=b;
                  b:=a;
                  a:=t;
                end;
    while a mod b<>0 do
    begin
      a:=a mod b;
      t:=a;a:=b;b:=t;
    end;
    ys:=b;
  end;
procedure run;
  var i:integer;
  begin
    for i:=1 to n-1 do
    begin
      readln(m);
      pd(m0,m);
      m0:=ys;
    end;
    writeln(ys);
  end;
begin
  readln(n);
  read(m0);
  run;
end.

Maybe replace readln to read