#include <bits/stdc++.h>

using namespace std;

int query(int x)
{
    cout <<"? "<<x<<endl;
    int ans;
    cin >>ans;
    return ans;
}

int n,st,dr;

int main()
{
    cin >>n;
    st = 1;
    dr = n;
    while(st <= dr)
    {
        int mid = (st+dr)/2;
        if(query(mid) == 1)
        {
            dr = mid-1;
        }
        else
        {
            st = mid+1;
        }
    }
    cout <<"! "<<st<<endl;
    return 0;
}