#include <bits/stdc++.h>
using namespace std;
#define int long long
#define ll long long
#define ar array
#define ld long double
const int N = 3e5 + 20;
const int B = 400;
const int M = 200;
const int INF = 1e15;
const int LOG = 24;
const int MOD = 998244353;
#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx,bmi,bmi2,lzcnt,popcnt")
bool query(int x){
cout<<"? "<<x<<endl;
int res;
cin>>res;
return res;
}
signed main(){ios_base::sync_with_stdio(false);cin.tie(0);
int n;
cin>>n;
int l = 0;
int r = n;
vector<int> v;
while(l + 1 < r)v.push_back((l + r) / 2), l = (l + r) / 2;
int pos = 1;
reverse(v.begin(), v.end());
for(auto u: v){
if(pos + u <= n)pos += u;
else pos -= u;
}
map<int,bool> vis;
vis[pos] = 1;
l = 0, r = n;
query(pos);
while(l +1 < r){
int mid = (l + r)/ 2;
if(pos + mid <= n && !vis[pos + mid]){
pos += mid;
}else pos -= mid;
vis[pos] = 1;
if(query(pos))r = mid;
else l = mid;
}
cout<<"= "<<r<<endl;
}
