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