program acm1909;
var
 n,i,t,top:integer; ch:string;
 a:array[1..10000]of longint;
begin
 readln(n);
 while n<>0 do
  begin
   top:=0;
   for i:=1 to n do
    begin
     readln(ch);
     if ch[1]='P' then
      begin
       ch:=copy(ch,2,length(ch));
       val(ch,t);
       inc(top); a[top]:=t;
      end;
     if (ch[1]='O')and(top>0) then dec(top);
     if ch[1]='A' then
      begin
       if top=0 then writeln('E')
        else writeln(a[top]);
      end;
    end;
   writeln;
   readln(n);
  end;
end.
/**************************************************************
	Problem: 2192
	User: admin
	Language: Pascal
	Result: Wrong Answer
****************************************************************/