#include <bits/stdc++.h>
using namespace std;
string np = "text";
ifstream f(np + ".in");
ofstream g(np + ".out");

#define f cin
#define g cout

int n, st = 1, dr, rez;

int main()
{
    f >> dr;
    while (st <= dr)
    {
        int mid = (st + dr) / 2, aux;

        g << "? " << mid << '\n';
        f >> aux;

        if (aux)
            rez = mid, dr = mid - 1;
        else
            st = mid + 1;
    }
    g << "! " << rez;

    return 0;
}