program cbinteractiv;
var n : longint;
var lo, hi, mid : longint;
var answer : longint;

begin
readln(input, n);

lo := 1;
hi := n;

while lo < hi do
begin
    mid := (lo + hi) div 2;
    
    writeln(output, '? ', mid);
    flush(output);

    readln(input, answer);

    if answer = 1 then
        hi := mid
    else
        lo := mid + 1;

end;

writeln(output, '! ', lo);
flush(output);

end.