#include <iostream>

using namespace std;

int main()
{
    int n,st,dr,mid;
    cin>>n;
    st=1,dr=n;
    while(st!=dr)
    {
        bool lower;
        mid=(st+dr)/2;
        cout<<"? "<<mid<<'\n';
        cout.flush();
        cin>>lower;
        if(lower) dr=mid;
        else st=mid+1;
    }
    cout<<st;
    return 0;
}