#include <iostream>
using namespace std;

int main()
{
    int n, l, r, mij, rasp;
    cin >> n;
    l = 1, r = n;
    while (l < r) {
        mij = (l + r) / 2;
        cout << "? " << mij << endl;
        cin >> rasp;
        if (rasp == -1) return 0;
        else if (rasp == 0) l = mij + 1;
        else r = mij;
    }
    cout << "! " << l << endl;
}