#include <bits/stdc++.h>

using namespace std;

int n, x, k, ans;

int F(int x, int k){
    int val;
    cout << "? " << x << "\n";
    cin >> val;
    return val;
}

void Cb(){
    int st, dr, mij;
    st = 1;
    dr = n;
    while(st <= dr){
        mij = (st + dr) / 2;
        if(F(mij, ans)){
            ans = mij;
            dr = mij - 1;
        }
        else
            st = mij + 1;
    }
}

int main()
{
    cin >> n;
    Cb();
    cout << "! " << ans << "\n";
    return 0;
}