#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <cmath>
#include <bitset>
#include <unordered_map>
#include <stack>
#include <random>
using namespace std;
const int N = 300003;
const int mod = 1e9 + 7;
int query(int x)
{
cout << "? " << x << endl;
int res;
cin >> res;
return res;
}
void solve()
{
int l = 1, r;
cin >> r;
while (l < r)
{
int m = (l + r) / 2;
int p = query(m);
if (p == -1)
l = m + 1;
else if (p == 1)
r = m - 1;
else
l = r = m;
}
cout << "= " << l << endl;
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(0);
cout.tie(0);
int t = 1;
//cin >> t;
while (t--)
solve();
return 0;
}
