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

int main()
{
    int n;
    cin >> n;
    int lb=1, rb=n;
    while(lb<=rb)
    {
        if(lb==rb)
        {
            cout << "! " << lb << endl;
            return 0;
        }
        int mb=(lb+rb)/2, judge;
        cout << "? " << mb << endl;
        cin >> judge;
        if(judge==1)
            rb=mb;
        else
            lb=mb+1;
    }
    return 0;
}