#pragma GCC target("avx")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	int N;
	cin >> N;
	for( int i = 0; i+1 < N; i+=2 ) {
		int z;
		cout << "? " << i << ' ' << i+1 << endl;
		cin >> z;
		if( z == i ) {
			cout << "! " << i+1 << endl;
			return 0;
		}else if( z == i+1 ) {
			cout << "! " << i << endl;
		}
	}
	cout << "! " << N-1 << endl;
}