var n,m,x,i:longint;
    b:array[0..10100]of longint;
  begin
    readln(n,m);
    for i:=1 to n do begin read(x);inc(b[x]);end;
    for i:=0 to m do 
      if b[i]>(n div 2) then begin writeln(i);halt;end;
    writeln('?');
  end.