#include<bits/stdc++.h>
#define inf 0x3f3f3f3f
#define rep(i, a, b) for (int i = a, i_end = b; i <= i_end; i++)
#define dep(i, a, b) for (int i = a, i_end = b; i >= i_end; i--)
#define VV vector<int>
#define PP pair<int,int>
#define ls (rt<<1)
#define rs (rt<<1|1)
#define fi first
#define se second
#define pb push_back
using namespace std;
typedef long long ll;
template <typename T>
inline void read(T &X){
    X=0;int w=0; char ch=0;
    while(!isdigit(ch)) {w|=ch=='-';ch=getchar();}
    while(isdigit(ch)) X=(X<<3)+(X<<1)+(ch^48),ch=getchar();
    if(w) X=-X;
}
const int maxn=4e5+5;
//const double pi=acos(-1.0);
//const double eps=1e-9;
//const ll mo=1e9+7;
int n,m,k;
int a[maxn],c[maxn];
int ans,tmp,cnt;
int flag;
char s[maxn];
bool ok[maxn];
int qry(int x){
	cout << "? " << x << endl;
	int y;
	cin >> y;
	return y;
}
void prt(int x){
	cout << "! " << x << endl;
}
void solve(){
    read(n);
	a[0] = a[n + 1] = inf;
	if(n<1){
		rep(i,1,n){
			a[i] = qry(i);
		}
		rep(i,1,n) if(a[i]<a[i-1]&&a[i]<a[i+1]){
			prt(i);
			break;
		}
		return;
	}
	int l = 1, r = n;
	while(l<=r){
		int mid = (l + r) / 2;
		int x = (mid > 1) ? qry(mid - 1) : inf;
		int y = qry(mid);
		int z = (mid < n) ? qry(mid + 1) : inf;
		if(x>y&&y<z) {
			prt(mid);
			return;
		}
		if(x<=z)
			r = mid;
		else
			l = mid + 1;
	}
}
int main(){
    // freopen("e://duipai//amyout.txt","w",stdout);
    int T=1,cas=1;
    //read(T);
    while(T--){
        solve();
    }
    //system("pause");
    return 0;
}
