#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
  #define _GLIBCXX_DEBUG
#else
  #define Debug(...) void(0)
#endif
using ll = long long;
#define rep(i, n) for (int i = 0; i < (n); ++i)

int Query(int x, int y) {
  printf("? %d %d\n", x, y);
  fflush(stdout);
  int z;
  cin >> z;
  return z;
}

int main() {
  int n;
  cin >> n;
  vector<bool> a(n, false);
  rep(i, n / 2) {
    if (a[i]) continue;
    int z = Query(2 * i, 2 * i + 1);
    if (z == 2 * i || z == 2 * i + 1) {
      printf("! %d\n", z ^ 1);
      fflush(stdout);
      return 0;
    }
  }
  printf("! %d\n", n - 1);
  fflush(stdout);
  return 0;
}