#include <bits/stdc++.h>
using namespace std;
int main(int argc, char const *argv[])
{
int N;
cin >> N;
vector<int> pos(N);
iota(pos.begin(), pos.end(), 1);
cout << "? " << pos.size() << endl;
int prev = pos.size();
int answer;
cin >> answer;
bool broken = false;
while(pos.size() > 1)
{
int current = pos[(pos.size() / 2)];
cout << "? " << current << endl;
cin >> answer;
if (answer == 1)
{
pos.resize(abs(prev - current));
}
else
{
pos.erase(pos.begin(), pos.begin() + (pos.size() / 2));
}
prev = current;
}
if (!broken) cout << "= " << pos[0] << endl;
return 0;
}
