#include <bits/stdc++.h>
using namespace std;
void cb (int st, int dr)
{
    int mij = (st + dr) / 2;
    if(st < dr)
    {
        cout << "? " << mij << '\n';
        cout.flush();
        int ver;
        cin >> ver;
        if(ver == 0) cb(mij + 1, dr);
        else cb(st, mij - 1);
    }
    else
    {
        cout << "! " << mij;
        cout.flush();
    }
}
int main ()
{
    long long int n, st = 1, dr ;
    cin >> n;
    dr = n;
    cb(st, dr);
}