#include <bits/stdc++.h>

using namespace std;
using ll = long long;

bool ask( int val ) {
  int t;
  cout << "? " << val << endl;
  cin >> t;
  return t;
}

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int n;

  cin >> n;
  int l = 0, r = n;
  while ( r - l > 1 ) {
	int mid = (l + r) / 2;
	if ( ask(mid) ) {
	  r = mid;
	} else {
	  l = mid;
	}
  }
  cout << "! " << r << endl;
  return 0;
}