#include<bits/stdc++.h>
using namespace std;

int main(){
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  int N;
  cin>>N;
  for(int i=0;i<N-1;i+=2){
    cout<<"? "<<i<<' '<<i+1<<endl;
    int z;
    cin>>z;
    if(z==i){
      cout<<"! "<<i+1<<endl;
      return 0;
    }
    if(z==i+1){
      cout<<"! "<<i<<endl;
      return 0;
    }
  }
  cout<<"! "<<N-1<<endl;
}