#include <bits/stdc++.h>

#define x first
#define y second
#define el '\n'
#define debug(x) cout << #x << ": " << x << el
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
const int N = 5010, INF = 0x3f3f3f3f, mod = 998244353;

void inc(ll &a, ll b) {
    a += b;
    if (a >= mod) a -= mod;
}

void dec(ll &a, ll b) {
    a -= b;
    if (a < 0) a += mod;
}

ll add(ll a, ll b) {
    a += b;
    return a >= mod ? a - mod : a;
}

ll del(ll a, ll b) {
    a -= b;
    return a < 0 ? a + mod : a;
}

int ask(int x) {
    cout << "? " << x << endl;
    int res; cin >> res;
    return res;
}

void quit(int x) {
    cout << "! " << x << endl;
    exit(0);
}

int main() {
    // ios::sync_with_stdio(0); cin.tie(0);
    int n; cin >> n;
    int last = 0;
    for (int i = 1; i <= 20; ++i) {
        int x = ask(i);
        if (x == last) quit(i);
        last = x;
    }
    int l = 21, r = n;
    while (l < r) {
        int mid = l + r >> 1;
        int x = ask(mid);
        if (x == last) quit(mid);
        if (x > last) l = mid + 1;
        else r = mid - 1;
        last = mid;
    }
    cout << "! " << l << endl;
}