#include <bits/stdc++.h>
using namespace std;
// #define int long long
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<int, int> p11;
typedef pair<string, int> ps1;
typedef pair<ll, ll> p1111;
#define vv vector
#define pb emplace_back
#define IOS ios::sync_with_stdio(false); cin.tie(0); cout.tie(0)
#define fi first
#define se second
// #define endl '\n'
// #define Endl '\n'
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define per(a, b, c) for(int a = b; a <= c; a ++)
#define rep(a, b, c) for(int a = b; a >= c; a --)
#define aper(A) for(auto i : A) cout << i << ' ';cout << '\n'
#define lowbit(x) ((x) & (-x))
#define yes cout << "Yes" << endl
#define no cout << "No" << endl
#define YES cout << "YES" << endl
#define NO cout << "NO" << endl
#define PAI acos(-1)
using ll = long long;
#define double long double 
void umin(int &x,int y){if(x>y)x=y;}
void umax(int &x,int y){if(x<y)x=y;}
const int mod = 1e9 + 7;
void add(int &x, int y){x = (x + y) % mod;}
void pre_work(){}

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

void pri(int x)
{
    cout << "! " << x << endl;
}

void solve()
{
    int n;
    cin >> n;
    int pre = 0;
    for(int i = 1; i <= 19; i ++)
    {
        int now = ask(i);
        if(now == pre)
        {
            pri(i);
            return;
        }
        pre = now;
    }
    int l = 20, r = n;
    while(l <= r)
    {
        int mid = l + r + 1 >> 1;
        int x = ask(mid);
        if(x == pre)
        {
            pri(mid);
            return;
        }
        else if(x > pre)
        {
            l = mid + 1;
        }
        else 
        {
            r = mid - 1;
        }
        pre = x;
    }
}

signed main()
{
 	IOS;
	int tt = 1;
	//cin >> tt;
	pre_work();
	while(tt --)
	{
		solve();
	}
	return 0;
}