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

int main(){
    int n;
    cin>>n;
    for(int i = 0;i<n-1;i+=2){
        cout<<"? "<<i<<" "<<i+1<<endl;
        int x;
        cin>>x;
        if(x==i||x==i+1){
            if(x==i) x = i + 1;
            else x = i;
            cout<<"! "<<x<<endl;
            return 0;
        }
    }
    cout<<"! "<<n-1<<endl;
}