#include <iostream>
using namespace std;
int main(){
	int n, st, dr, mij, r;
	ios::sync_with_stdio( false );
	cin.tie( 0 );
	cout.tie( 0 );
	cin >> n;
	st = 0;
	dr = n;
	while( dr - st > 1 ){
		mij = ( st + dr ) / 2;
		cout << "? " << mij << '\n';
		cout.flush();
		cin >> r;
		if( r == 1 ){
			dr = mij;
		}
		else{
			st = mij;
		}
	}
	cout << "! " << dr << '\n';
	cout.flush();
	return 0;
}