#include<iostream>
using namespace std;
int n,k,m;
int main()
{
    for(cin>>n,m=1;m!=n;cout<<"? "<<(m+n)/2<<"\n",cout.flush(),cin>>k,k?n=(m+n)/2:m=(m+n)/2+1);
    return cout<<"! "<<m,cout.flush(),0;
}