#include <iostream>

using namespace std;
int query(int x)
{
    cout<<"?"<<x<<endl;
    int res;
    cin>>res;
    return res;
}
int main()
{
   int n;
   cin>>n;
   int left=1,right=n;
   while(left<=right)
   {
       int mid=(left+right)/2;
       if(query(mid)==1)
        right=mid-1;
       else left=mid+1;
   }
   cout<<"!"<<left;
    return 0;
}