#include <iostream>

using namespace std;
int n,k,m;
int query(int x)
{
    cout<<"? "<<x<<endl;
    int res;
    cin>>res;
    return res;

}
int main()
{
    cin>>n;
    int left=0,right=n;
    while(left<=right)
    {
        int mid=(left+right)/2;
        if(query(mid)==1)
        {
            right=mid-1;
        }else
        {
            left=mid+1;
        }

    }
    cout<<"! "<<left<<endl;
    return 0;
}