#include <iostream>
using namespace std;

int Query(int x)
{
    int rez;
    cout << "? " << x << endl;
    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;
}