#include <iostream>
using namespace std;

int main() {
  int dr, st, e, mij;
  cin >> dr;
  st = 0;
  while( dr - st > 1 ) {
    mij = ( st + dr ) / 2;
    cout << "? " << mij << endl;
    cin >> e;
    if( !e )
      st = mij;
    else
      dr = mij;
  }
  cout << "! " << dr;
  return 0;
}