#include <bits/stdc++.h>
using namespace std;
// #include <ext/pb_ds/assoc_container.hpp>
// #include <ext/pb_ds/tree_policy.hpp>
// using namespace __gnu_pbds;
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii ;
typedef pair<ll, ll> pll ;
typedef vector<pii> vii ;
typedef vector<int> veci ;
typedef vector<pll> vll ;
typedef vector<ll> vecll;
// find_by_order order_of_key
//#pragma GCC optimize("O3,unroll-loops")
//#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
#define F first
#define S second
#define pb push_back
#define Mp make_pair
#define all(x) x.begin(), x.end()
#define debug(x) cerr << #x << " = " << x << endl
#define set_dec(x) cout << fixed << setprecision(x);
#define fast_io ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define file_io freopen("in.txt" , "r" , stdin) ; freopen("out.txt" , "w" , stdout);
#define lb lower_bound
#define ub upper_bound
#define for1(n) for(int i=1;i<=n;i++)
#define for0(n) for(int i=0;i<n;i++)
#define forn(n) for(int i=n;i>0;i--)
#define pq priority_queue <pii, vector<pii>, greater<pii>>
int n,L,vis[1000];
bool ask(ll t){
if(t<=0 || t>n)exit(0);
cout<<"? "<<t<<endl;
bool o;cin>>o;
o^=1;
return o;
}
int main(){
cin>>n;
ll s=n,tmp=0;L=log2(n-1);
vector<ll>vec;
ll t=0;
while(t!=n-1){
t=(t+n)/2;
vec.pb(t);
}
reverse(all(vec));
for(ll x:vec){
if(s-x>0)
s-=x;
else
s+=x;
}
ask(s);
ll l=0,r=n;
while(r-l!=1){
ll mid=(l+r)>>1;
ll ss=s;
if(ss<=n/2)ss+=mid;
else ss-=mid;
if(ask(ss))l=mid;
else r=mid;
s=ss;
}
cout<<"= "<<l+1<<endl;
}
