#include <iostream>

using namespace std;

int n;

void cautbin(int from, int to){
  if(from >= to){
    cout << "! " << from << "\n";cout.flush();
  }else{
    int mid = (from + to) / 2, c;
    cout << "? " << mid << "\n";cout.flush();
    cin >> c;
    if(c == 1){
      cautbin(from, mid);
    }else{
      cautbin(mid+1, to);
    }
  }
}

int main() {

  cin >> n;
  cautbin(1, n);
  return 0;
}