#include<bits/stdc++.h>
using namespace std;
#define int long long
#define inf (int)2e18
#define _ <<' '<<
#define nl endl
int qry(int x){
cout<<"? "<<x<<nl;
cin>>x;
return x;
}
void solve(){
int n;
cin>>n;
int l = 1, r = n, cur = 0, t = 0, mn = 0;
while(l < r){
int m = (l+r)/2;
if(t) cur += m;
else cur -= m;
t = !t;
mn = min(mn, cur);
l = m+1;
}
l = 1, r = n, cur = 1 - mn, t = 0;
qry(cur);
while(l < r){
int m = (l+r)/2;
if(t) cur += m;
else cur -= m;
t = !t;
if(qry(cur)) r = m;
else l = m+1;
}
cout<<"= "<<l<<nl;
}
signed main(){
ios_base::sync_with_stdio(0);
cin.tie(NULL);cout.tie(NULL);
int t = 1;
//cin>>t;
while(t--) solve();
return 0;
}
