#include <bits/stdc++.h>

using namespace std;

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

  int lo = 1, hi = n;
  int guess, feedback, ans;
  while (lo <= hi) {
    guess = (lo + hi) / 2;
    cout << "? " << guess << '\n';
    cout.flush();
    cin >> feedback;
    if (feedback == 0)
      lo = guess + 1;
    else {
      ans = guess;
      hi = guess - 1;
    }
  }
  cout << "! " << ans << '\n';
  cout.flush();
  return 0;
}