#include <bits/stdc++.h>
using namespace std;
long long n;
int ans;
int main (void){
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
cin >> n;
long long mini = 0;
long long maxi = (n - 1) / 32;
long long pola = (mini + maxi + 1) / 2;
int prosli = -1;
if (maxi % 2 == 0){
cout << "? " << pola * 32 + 1 << endl;
cin >> ans;
for (int i = 1; i <= maxi - pola; i++){
cout << "? " << (pola + i) * 32 + 1 << endl;
cin >> ans;
if (ans == 1 and prosli == -1) prosli = 2 * i - 1;
cout << "? " << (pola - i) * 32 + 1 << endl;
cin >> ans;
if (ans == 1 and prosli == -1) prosli = 2 * i;
}
}
else{
for (int i = 0; i <= maxi - pola; i++){
cout << "? " << (pola + i) * 32 + 1 << endl;
cin >> ans;
if (i != 0 and ans == 1 and prosli == -1) prosli = 2 * i + 1;
cout << "? " << (pola - i - 1) * 32 + 1 << endl;
cin >> ans;
if (ans == 1 and prosli == -1) prosli = 2 * i + 2;
}
}
long long rez, tr, zadnji, granica;
if (prosli == -1){
rez = n;
tr = n - 1;
zadnji = 1;
granica = maxi * 32;
}
else{
rez = prosli * 32;
tr = prosli * 32 - 1;
zadnji = 1;
granica = prosli * 32 - 32;
}
while (tr > granica){
cout << "? " << zadnji + tr << endl;
cin >> ans;
if (ans == 1) rez--;
zadnji += tr;
tr--;
if (tr == granica) break;
cout << "? " << zadnji - tr << endl;
cin >> ans;
if (ans == 1) rez--;
zadnji -= tr;
tr--;
}
cout << "= " << rez << endl;
return 0;
}
