#include <iostream>
#include <set>
using namespace std;

int main(){
    int n;cin>>n;
    set<int> A;
    int c = 0;
    for(int i = 0; n > i; i++){
        if(A.count(i))continue;
        if(n/2 == c){
          cout << "! " << i << endl;
          return 0;
        }
        cout << "? " << i << " " << i << endl;
        c++;
        int x;cin>>x;
        if(i==x){
            cout << "! " << i << endl;
            return 0;
        }
        A.insert(x);
    }
}