#include <iostream>
using namespace std;

int main() {

    int n;

    cin >> n;

    int st = 1, dr = n, aux;

    while (st < dr) {

        int mij = (st + dr) / 2;

        cout << '?' << mij << '\n';

        cin >> aux;

        if (aux == 1) dr = mij;
        else st = mij + 1;
    }

    cout << '!' << st;

    return 0;
}