#include "bits/stdc++.h"
using namespace std;
#define INF 1000000000
#define INFLL 1000000000000000000ll
#define EPS 1e-9
#define all(x) x.begin(),x.end()
#define rall(x) x.rbegin(),x.rend()
#define pb push_back
#define fi first
#define sc second
using i64 = long long;
using u64 = unsigned long long;
using ld = long double;
using ii = pair<int, int>;
int query(int p) {
int ans;
cout << "? " << p << endl;
cin >> ans;
return ans;
}
void answer(int p) {
cout << "= " << p << endl;
exit(0);
}
void solve() {
int n;
cin >> n;
int l = 1, r = n + 1;
while(l < r) {
int m = (l + r) / 2;
int ans = query(m);
if(ans > 0) r = m;
else if(ans < 0) l = m + 1;
else answer(m);
}
}
int main() {
ios_base :: sync_with_stdio(false);
//cin.tie(0);
int t = 1;
//cin >> t;
while(t--) solve();
return 0;
}
