#include <stdio.h>
#include <stdlib.h>

int main()
{
    int n;
    scanf("%d", &n);
    int st = 1, dr = n;
    while (st < dr)
    {
        int m = (st + dr) / 2;
        printf("? %d\n", m);
        fflush(stdout);
        int raspuns;
        scanf("%d", &raspuns);
        if (raspuns == -1)
        {
            return 0;
        }
        if (raspuns == 0)
        {
            st = m + 1;
        }
        else
        {
            dr = m;
        }
    }
    printf("! %d\n", st);
    fflush(stdout);
    return 0;
}