#pragma GCC optimize("O3")
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ld long double
#define pb push_back
#define ff first
#define ss second
#define MOD 998244353LL
#define INF 1000000001LL
#define POT (1LL<<20)
#define INFL 1000000000000000099LL
#define pii pair<ll,ll>
#define ppi pair<pii,ll>
#define pip pair<ll,pii>
#define ppp pair<pii,pii>
#define vi vector<ll>
#define vii vector<pii>
#define al(x) x.begin(),x.end()
#define rev(x) reverse(al(x))
#define X 18
template<typename T, typename U>
pair<T, U> operator+(const pair<T, U>& a, const pair<T, U>& b) {
return {a.first + b.first, a.second + b.second};
}
template<typename T, typename U>
pair<T, U> operator-(const pair<T, U>& a, const pair<T, U>& b) {
return {a.first - b.first, a.second - b.second};
}
template<typename T, typename U>
ostream& operator<<(ostream& os, const pair<T, U>& p) {
os<<"{"<<p.ff<<", "<<p.ss<<"}";
return os;
}
template<typename T>
ostream& operator<<(ostream& os, const vector<T>& v) {
os << "{";
for (size_t i = 0; i < v.size(); ++i) {
if (i) os << ", ";
os << v[i];
}
os << "}";
return os;
}
ll fct[1000007];
ll fp(ll a,ll b){
ll c=1;while(b){if(b&1)c=(c*a)%MOD;a=(a*a)%MOD;b/=2;}
return c;
}
ll n,a=2,d,z=0;
ll t=1;
ll pp;
ll gtn(){
cin>>a;
return a;
}
bool query(ll x){
cout<<"? "<<x<<endl;
bool ns;
cin>>ns;return ns;
}
void ns(ll x){
cout<<"= "<<x<<"\n";
}
void solve(){
n=gtn();
ll ps=0;
ll x=n;
while(x!=1){
//cout<<n-(x+1)/2<<" "<<x<<" ";
ps=(n-(x+1)/2)-ps;
x=(x+1)/2;
}
ps=min(ps+1,n-ps);
//cout<<ps<<"\n";
query(ps);
ll ak=0;
x=n;
ll y=1;
while(x!=1){
//cout<<x/2+ak<<"\n";
ps+=y*(x/2+ak);
y=-y;
if(!query(ps)){
ak+=(x/2);
x-=x/2;
}
else{
x/=2;
}
}
ns(ak+1);
}
int main(){
fct[0]=1;
for(ll i=1;i<1000007;i++)fct[i]=(fct[i-1]*i)%MOD;
//cin>>t;
for(ll i=1;i<=t;i++){
//cout<<"Case #"<<i<<": ";
solve();
}
}
