#include<stdio.h>
int d,s,o,m;
int main()
{
    for(scanf("%d",&d),s=1;s<=d;) {
        m=(s+d)>>1,printf("? %d\n",m),fflush(stdout),scanf("%d",&o);
        if(!o)
            s=m+1;
        else
            d=m-1;
    }
    printf("! %d",s),
    fflush(stdout);
    return 0;
}