#include<bits/stdc++.h>
#define int int64_t
using namespace std;
const int maxn = 2e5+10;
bool qry(int x){
	cout<<"? "<<x<<endl;
	bool res;cin>>res;return res;
}
void sol(){
	int n;cin>>n;
	int cur=0;

{
	int l=1,r=n;
	set<int>qed;
	qed.insert(cur);
	while(l<r){
		int md=(l+r)>>1;
		// if(stp^=1)cur+=md;
		// else cur-=md;
		// deb(cur+md,cur-md);
		if(cur+md>n)cur-=md;
		else if(cur-md<=0)cur+=md;
		else if(qed.count(cur+md))cur-=md;
		else if(abs(cur+md-(1+n)/2.) < abs(cur-md-(1+n)/2.))cur+=md;
		else cur-=md;
		qed.insert(cur);
		if(0)r=md;
		else l=md+1;
	}
	cur=1-*qed.begin();
}

	int l=1,r=n;
	set<int>qed;
	qry(cur);qed.insert(cur);
	while(l<r){
		int md=(l+r)>>1;
		// if(stp^=1)cur+=md;
		// else cur-=md;
		// deb(cur+md,cur-md);
		while(cur+md>n&&cur-md<=0)--md;
		if(cur+md>n)cur-=md;
		else if(cur-md<=0)cur+=md;
		else if(qed.count(cur+md))cur-=md;
		else if(abs(cur+md-(1+n)/2.) < abs(cur-md-(1+n)/2.))cur+=md;
		else cur-=md;
		qed.insert(cur);
		if(qry(cur))r=md;
		else l=md+1;
	}
	cout<<"= "<<r<<endl;
}

signed main() {
	// ios::sync_with_stdio(0),cin.tie(0);
	// int T;cin>>T;while(T--)
	sol();
	// const int n=8;
	// int len=n / 2;
	// int cur=0;int stp=0;
	// set<int>se;
	// while(len < n){
	// 	deb(len,cur);

	// 	assert(se.insert(cur).second);
	// 	if(stp^=1)cur+=len;
	// 	else cur-=len;
	// 	int nl=(1+len+n)/2;
	// 	len=nl;
	// }
	// se.insert(cur);

	// deb(se,se.size());
}