#include <bits/stdc++.h>
using namespace std;
#define int              long long int
#define double           long double
#define print(a)         for(auto x : a) cout << x << " "; cout << endl


const int M = 1000000007;
const int N = 3e5+9;
const int INF = 2e9+1;
const int LINF = 2000000000000000001;

inline int power(int a, int b, int mod=M) {
    int x = 1;
    a %= mod;
    while (b) {
        if (b & 1) x = (x * a) % mod; 
        a = (a * a) % mod;
        b >>= 1;
    }
    return x;
}


//_ ***************************** START Below *******************************

//* Change this to false => before submitting to cf
// bool testing = true; 
bool testing = false;


vector<int> a;

void hack(int n){
    a.resize(n+1);
    for(int i=1; i<=n; i++) cin >> a[i];
}

int  interactor(int i){
    return a[i];
}



int askQuery(int x){
    cout << "? " << x << endl;

    if(testing){
        cout << interactor(x) << endl;
        return interactor(x);
    }
    int y;
    cin >> y;
    return y;

}


int consistency(int n){

    if(testing){
        hack(n);
    }

    int s = 1, e = n;
    int ans = -1;

    while(s<=e){
        int mid = s + (e-s)/2;


        int res = askQuery(mid);
        int left = mid-1 == 0 ? INF : askQuery(mid-1);
        int right = mid+1 == n+1 ? INF : askQuery(mid+1);

        if(left > res && res < right){
            ans = mid;
            break;
        }
        if(left > res ){
            s = mid+1;
        }
        else{
            e = mid-1;
        }

    }

    return ans;
}








void solve() {
    int n;
    cin >> n;

    int ans = consistency(n);
    cout << "! " << ans << endl;

}





int32_t main() {
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

    int t = 1;
    // cin >> t;
    while(t--){
        solve();
    }


    return 0;
}