#include <bits/stdc++.h>
using namespace std;
int main()
{
    int st, dr, mij, x;
    scanf("%d", &dr);
    st = 0;
    while (dr - st > 1) {
        mij = (st + dr) / 2;
        printf("? %d\n", mij);
        fflush(stdout);
        scanf("%d", &x);
        if (x == 0) {
            st = mij;
        } else {
            dr = mij;
        }
    }
    printf("! %d\n", dr);
    return 0;
}