#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;
using mint = modint998244353;

int main() {
  int N, z; cin >> N;
  if (N % 2 == 0) {
    for (int i = 0; i < N; i += 2) {
      cout << "? " << i << ' ' << i + 1 << endl;
      cin >> z;
      if (z == i) { cout << "! " << i + 1 << endl; return 0; }
      if (z == i + 1) { cout << "! " << i << endl; return 0; }
    }
  } else {
    for (int i = 0; i < N - 1; i += 2) {
      cout << "? " << i << ' ' << i + 1 << endl;
      cin >> z;
      if (z == i) { cout << "! " << i + 1 << endl; return 0; }
      if (z == i + 1) { cout << "! " << i << endl; return 0; }
    }
    cout << "! " << N - 1 << endl;
  }
  ;
  return 0;
}