#include <iostream>

using namespace std;

int query(int X)
{
    cout<<"? "<<X<<'\n';
    int res;
    cin>>res;
    return res;
}

int main()
{
    long long n,st=1,dr,mij;
    cin>>n;
    dr=n;
    while(st<=dr)
    {
        mij=(st+dr)/2;
        if(query(mij)==1)
        {
            dr=mij-1;
        }
        else
        {
            st=mij+1;
        }
    }
    cout<<"!"<<st;

    return 0;
}