#include <bits/stdc++.h>
using namespace std;

int n, x, xx;

int main()
{
    cin >> n;
    cout << "? 1\n";
    cout.flush();
    cin >> x;
    if (x == 0)
    {
        cout << "! 1\n";
        cout.flush();
        return 0;
    }
    int t = 40, l = 2, r = n;
    while (l <= r)
    {
        int mid = (l + r) >> 1;
        cout << "? " << mid << "\n";
        cout.flush();
        cin >> xx;
        // cout<<"- "<<xx<<"\n";
        if (xx < x)
        {
            r = mid - 1;
        }
        else if (xx > x)
        {
            l = mid + 1;
        }
        else
        {
            cout << "! " << mid << "\n";
            cout.flush();
            break;
        }
        x = xx;
    }

    return 0;
}