#include <iostream>
using namespace std;
int main () {
    int n;
    cin >> n;
    int st = 1, dr = n, mij, ans;
    while ( st < dr ) {
        mij = ( st + dr ) / 2;
        cout << "? " << mij << endl;
        cin >> ans;
        if ( ans == 0 )
            st = mij + 1;
        else
            dr = mij;
    }
    cout << "! " << st << endl;
    
    return 0;
}