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

#define VMIN 0
#define VMAX 1000000000

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