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#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <math.h>
#include <string>
using namespace std;







int main()
{
    cout.flush();



    int n,gl,gp,m,mz,k;
    k = 0;
    cin >> n;
    gl = 1; gp = n;
    cout << "? " << 1 << endl;
    cin >> mz;
    if (mz == 1) {
        cout << "! " << n;
        k++;
    }

    cout << "? " << n << endl;
    cin >> mz;
    if (mz == 0) {
        cout << "! " << 0;
        k++;
    }

    if (k == 0) {
        while (gp - gl > 1)
        {
            m = (gp + gl) / 2;
            cout << "? " << m << endl;
            cin >> mz;
            if (mz == 0)
                gl = m;
            if (mz == 1)
                gp = m;

        }
        cout << "! " << n - gp + 1;
    }








    return 0;
}