#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll, ll> pll;
#define all(x) (x).begin(),(x).end()
#define X first
#define Y second
#define sep ' '
#define debug(x) cerr << #x << ": " << x << endl;
const ll MAXN = 1e6 + 10;
const ll INF = 8e18;
const ll MOD = 1e9 + 7; // 998244353; // 1e9 + 9;
int main() {
ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
int n;
cin >> n;
int L = 1, R = n;
while (L <= R) {
int mid = (L + R) >> 1;
cout << "? " << mid << endl;
int ans;
cin >> ans;
if (ans == 0) return cout << "= " << mid << endl, 0;
else if (ans == 1) R = mid - 1;
else L = mid + 1;
}
return 0;
}
