#include <iostream>

using namespace std;

int main()
{
    int n,st,dr,mijl,rasp;
    cin>>n;
    st=1;
    dr=n;
    while (st<dr)
    {
        mijl=(st+dr)/2;
        cout<<"? "<<mijl<<endl;
        cin>>rasp;
        if (rasp==0)
            st=mijl+1;
        else
            dr=mijl;
    }
    cout<<"! "<<st<<endl;
    return 0;
}