#include <iostream>

using namespace std;

int main(void) {
  int n;
  cin >> n;

  for (int i = 0; i < n/2; ++i) {
    int a = i * 2;
    int b = i * 2 + 1;

    cout << "? " << a << " " << b << endl;

    int z;
    cin >> z;

    if (b == z) {
      cout << "! " << a << endl;
      return 0;
    } else if (a == z) {
      cout << "! " << b << endl;
      return 0;
    }
  }

  cout << "! " << n-1 << endl;
  return 0;
}