#include <bits/stdc++.h>

using namespace std;

int n;

int main()
{
    cin>>n;
    int st=1,dr=n,rasp=-1;
    while(st<dr)
    {
        int mij=(st+dr)/2;
        cout<<"? "<<mij;
        cout<<"\n";
        cout.flush();
        int q;
        cin>>q;
        if(q==0) st=mij+1;
        else if(q==1) dr=mij;
        else return 0;
    }
    cout<<"! "<<st;
    return 0;
}