#include <bits/stdc++.h>

using namespace std;
const int N = 1e9 + 9;

int n;

int main()
{
    cin >> n;

    int st = 1, dr = n;
    int res;
    while(st != dr)
    {
        int m = (st + dr) / 2;
        printf("? %d\n", m);
        fflush(stdout);

        scanf("%d\n", &res);
        if(res == 0)st = m + 1;
        else dr = m;
    }

    printf("! %d\n", st);
    fflush(stdout);
    return 0;
}