program binSearch;
uses crt;

var hi,lo,n,m,nume:integer;

begin
read(n);
     lo:=1;
     hi:=n;
     while (lo <> hi) do
     begin
           m:=(lo+hi) DIV 2;
           write(output, '? ');
           writeLn(output, m);
           flush(output);
           read(nume);
           if (nume = 0) then
            lo:=m+1
           else
            hi:=m;
     end;
     Write(output, '! ');
     writeLn(output, lo); 
     flush(output);
end.