#include <iostream>
using namespace std;
int main()
{
    int n;
    cin>>n;
    int st=1,dr=n,val=0;
    while(st<=dr){
        int mid=(st+dr)/2;
        cout<<"? "<<mid<<'\n';
        cout.flush();
        int ans;
        cin>>ans;
        if(ans==-1)
            return 0;
        else if(ans==0)
            st=mid+1;
        else
            dr=mid-1,val=mid;
    }
    cout<<"! "<<val<<'\n';
    cout.flush();
    return 0;
}