#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i,n) for (int i=0;i<(int)(n);i++)

int main(){
  int n;
  cin>>n;
  int ct=(n/2);
  rep(i,ct){
    cout<<"? "<<i*2<<" "<<i*2+1<<endl;
    int z;
    cin>>z;
    if(z==i*2){
      cout<<"! "<<i*2+1<<endl;
      return 0;
    }
    if(z==i*2+1){
      cout<<"! "<<i*2<<endl;
      return 0;
    }
  }
  cout<<"! "<<ct*2<<endl;
}