#include<bits/stdc++.h>
#pragma GCC optimize(2)
using namespace std;
using ll = long long;
using pii = pair<int, int>;
using tiii = tuple<int, int, int>;
int cnt = 0;
int q(int x) {
    int last = cnt;
    cout << "? " << x << endl;
    cin >> cnt;
    if (cnt == last) {
        cout << "! " << x << endl;
        return 0;
    } else if (cnt == last - 1) {
        return 1; 
    } else if (cnt == last + 1) {
        return -1;
    }
}
int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    int n; cin >> n;
    int l = 0, r = n;
    for (int i = 1; i <= 20; i++) {
        if (q(i) == 0) {
            return 0;
        }
    }
    while (1) {
        int mid = l + r >> 1;
        int qval = q(mid);
        if (qval == 0) {
            return 0;
        }
        else if (qval == 1) {
            l = mid;
        }
        if (qval == -1) {
            r = mid;
        }
    }
    return 0;
}