#include <bits/stdc++.h>

using namespace std;

bool query(int x) {
  cout << "? " << x << endl;
  bool ans;
  cin >> ans;
  return ans;
}

int main() {
  int N;
  cin >> N;
  int st = 1, dr = N, ans = N;
  while (st <= dr) {
    int mid = (st + dr) >> 1;
    bool rez = query(mid);
    if (rez) {
      ans = mid;
      dr = mid - 1;
    } else st = mid + 1;
  }
  cout << "! " << ans << endl;
  return 0;
}