#include <iostream>

using namespace std;

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

int main() {
  int n;
  cin >> n;
  int st = 1, dr = n, m;
  while (st < dr) {
    m = (st + dr) / 2;
    if (query(m))
      dr = m;
    else
      st = m + 1;
  }
  cout << "! " << st << endl;
  return 0;
}