#include "bits/stdc++.h"
using namespace std;
#define int long long
signed main () {
int n;
cin >> n;
int l = 1, r = n+2, f = 1;
cout << "? " << 1 << endl;
int x;
cin >> x;
if(n > 64) {
return 0;
}
while(1) {
if(l+1>=r)break;
if(f == 1) {
r -= 2;
cout << "? " << r << endl;
cin >> x;
if(x == 0) {
cout << "? " << l-1 << endl;
int x;
cin >> x;
if(x == 1) {
cout << "= " << r-(l-1) << endl;
}else {
cout << "= " << r-(l-2) << endl;
}
return 0;
}
f = -1;
}else {
l += 2;
cout << "? " << l << endl;
cin >> x;
if(x == 0) {
cout << "? " << r+1 << endl;
int x;
cin >> x;
if(x == 1) {
cout << "= " << r+1-l << endl;
}else {
cout << "= " << r+2-l << endl;
}
return 0;
}
f=1;
}
}
cout << "= 1" << endl;
return 0;
}
