#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef pair<ll,ll> P;
typedef vector<ll> VI;
typedef vector<VI> VVI;
#define REP(i,n) for(int i=0;i<(n);i++)
#define ALL(v) v.begin(),v.end()
template<typename T> bool chmax(T& x, const T& y){return (x<y)?(x=y,true):false;};
template<typename T> bool chmin(T& x, const T& y){return (x>y)?(x=y,true):false;};
constexpr ll MOD=998244353;
constexpr ll INF=2e18;

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