program cbinteractiva;
var n : longint;
var guess, step, nguess : longint;
var answer : longint;

begin
readln(input, n);

guess := 0;
step := (1 << 30);

while step <> 0 do
begin
    nguess := guess + step;

    if nguess <= n then
    begin
        write(output, '? ');
        writeln(output, nguess);
        flush(output);

        readln(input, answer);

        if answer = 0 then
        begin
            guess := nguess
        end;
    end;

    step := step div 2;
end;

write(output, '! ');
writeln(output, guess + 1);
flush(output);

end.