#include<bits/stdc++.h>
using namespace std;
#define edl '\n'
#define re return
#define gcd __gcd
#define db double
#define fir first
#define sec second
#define MAX 1000006
#define ll long long
#define i64 __int128
#define inf 2147483647
#define MAXN 100000009 
#define pll pair<ll,ll>
#define pb push_back
#define vint vector<int>
#define pii pair<int,int>
#define ANS cout<<ans<<edl
#define No cout<<"No"<<edl
#define NO cout<<"NO"<<edl
#define hhh cout<<"hhh"<<edl
#define Yes cout<<"Yes"<<edl
#define YES cout<<"YES"<<edl
#define all(a,l,r) a+l,a+1+r
#define ull unsigned long long
#define INF 9223372036854775807
#define vpii vector<pair<int,int>>
#define sp(x) fixed << setprecision(x)
#define FOR(i,l,r) for(auto(i)=(l);(i)<=(r);++(i))
const ll mod = 1000000007;
ll qpow(ll n,ll m,ll mod)
{
	ll ans=1;if(n>mod) n%=mod;
	while(m>0){if(m&1) {ans*=n;ans%=mod;}
	n*=n; n%=mod; m>>=1;} return ans;
}

void Solve(void)
{
	int n; cin>>n;
	int l=1, r=n, mid=l+r>>1, ans, pre=0;
	FOR(i,1,20) {
		cout<<"? "<<i<<endl;
		cin>>ans;
		if(ans==pre) {
			cout<<"! "<<i<<endl;
			re;
		}
		pre=ans;
	}
	l=21;
	while(l <= r) {
        ll mid = l + r >> 1;
		cout<<"? "<<mid<<endl;
		cin>>ans;
		if(ans==pre) {
			cout<<"! "<<1<<endl;
			re;
		}
		else if(ans>pre) {
			l=mid+1;
		}
		else if(ans<mid) {
			r=mid-1;
		}
		pre=ans;
    }
}
int main(void)
{
	std::ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
	int _=1;
	// cin>>_;
	while(_--)
    Solve ();
    return 0;
}