#include <bits/stdc++.h>

using namespace std;

int main() {
  int n;
  cin >> n;
  int p = 1, q = n + 1;
  for (; q - p > 1;) {
    int m = (p + q) >> 2;
    (cout << "! " << m).flush();
    int o;
    cin >> o;
    if (o == -1) {
      exit(1);
    } else {
      if (o) {
        q = m + 1;
      } else {
        p = m + 1;
      }
    }
  }
  (cout << "! " << p).flush();
  return 0;
}