#include<bits/stdc++.h>
namespace {
#pragma GCC diagnostic ignored "-Wunused-function"
#include<atcoder/all>
#pragma GCC diagnostic warning "-Wunused-function"
using namespace std;
using namespace atcoder;
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; i--)
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
template<class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } else return false; }
template<class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return true; } else return false; }
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;

int ask(int x, int y) {
  cout << "? " << x << ' ' << y << endl;
  int z;
  cin >> z;
  return z;
}

void answer(int k) {
  cout << "! " << k << endl;
}

} int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n;
  cin >> n;
  for(int i = 0; i + 1 < n; i += 2) {
    int z = ask(i, i + 1);
    if (z == i || z == i + 1) {
      int ans = z ^ i ^ (i + 1);
      answer(ans);
      return 0;
    }
  }
  answer(n - 1);
}