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

void answer(int x) {
    cout << '!' << ' ' << x << endl;
    exit(0);
}

int ask(int x) {
    cout << '?' << ' ' << x << endl;
    int ret;
    cin >> ret;
    return ret;
}

void solve(int l, int r, int lst) {
    int mid = (l + r) >> 1;
    if(l == r) {
        answer(l);
    }
    int x = ask(mid);
    if(x == lst) {
        answer(mid);
    }
    int y = ask(r);
    if(y == x) {
        answer(r);
    }
    if(x < y) {
        solve(l, max(l, mid - 1), y);
    }
    else {
        solve(min(r - 1, mid + 1), r - 1, y);
    }
    return;
}

int main() {
    int n;
    cin >> n;
    solve(1, n, 0);
    return 0;
}