#include <bits/stdc++.h>
using namespace std;
using ll = long long;
ll find_starting_point(ll size)
{
vector<ll> jumps;
ll L = 1;
while (L < size)
{
ll mid = L + (size - L + 1) / 2 - 1;
jumps.push_back(mid);
L = mid + 1;
}
ll epos = size;
int dir = -1;
reverse(jumps.begin(), jumps.end());
for (auto t : jumps)
{
epos = epos + dir * t;
dir = dir * -1;
}
if (dir == 1)
return epos;
return size - epos + 1;
}
ll solve_log(ll N, function<bool(ll)> query)
{
// Jump from Y + X to Y
// If 1
// Do solution X starting from y
// If 0
// Do solution (N - X) starting from y and expanding each query by Y
ll size = N;
ll pos = find_starting_point(N);
query(pos);
ll add = 0;
ll dir = 1;
while (size > 1)
{
ll jump_sz = size / 2;
ll inc_jump_sz = jump_sz + add;
pos = pos + inc_jump_sz * dir;
bool answ = query(pos);
if (answ)
{
size = jump_sz;
}
else
{
size = size - jump_sz;
add += jump_sz;
}
dir = dir * -1;
}
return add + 1;
}
bool query(ll pos)
{
int inp;
cout << "? " << pos << endl;
cin >> inp;
return inp == 1;
}
bool answer(ll pos)
{
cout << "= " << pos << endl;
exit(0);
}
int main()
{
ll N;
cin >> N;
answer(solve_log(N, query));
}
