#include <bits/stdc++.h>
using namespace std;
#define int long long
#define ld long double
#define show(x,y) cout << y << " " << #x << endl;
#define show2(x,y,i,j) cout << y << " " << #x << " " << j << " " << #i << endl;
#define show3(x,y,i,j,p,q) cout << y << " " << #x << " " << j << " " << #i << " " << q << " " << #p << endl;
#define show4(x,y) for(auto it:y) cout << it << " "; cout << #x << endl;
typedef pair<int,int>pii;
typedef pair<pii,int>pi2;
mt19937_64 rng(chrono::system_clock::now().time_since_epoch().count());
//int c=0;
int n=0;
//int lst=0;
set<int>se;
int f(int a){
cout << "? " << a << endl;
bool amos;
cin >> amos;
return amos;
//test
//if(se.find(a)!=se.end()){
//assert(0);
//}
//se.insert(a);
//bool hold = abs(a-lst) >= c;
//lst = a;
//return hold;
}
void solve(){
cin >> n;
int hold=n-n/2;
hold = hold/3*2 + hold%3;
//show(hold,hold);
int l=1;
int r=n-1;
int mid;
int best=n;
bool amos=true;
f(hold);
while(l<=r){
mid=(l+r)/2;
if(amos){
hold+=mid;
}
else hold-=mid;
amos=!amos;
if(f(hold)){
best=mid;
r=mid-1;
}
else l=mid+1;
}
//assert(best==c);
cout << "= " << best << endl;
}
int32_t main(){
ios::sync_with_stdio(0);
cin.tie(0);
//freopen("in.txt","r",stdin);
//freopen("in.txt","w",stdout);
int t=1;
//cin >> t;
while(t--){
solve();
}
}
