#include <bits/stdc++.h>
using namespace std;
#define fastio() cin.tie(0), ios_base::sync_with_stdio(0)
#define fileio() freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout)
#define pb push_back
#define pii pair<int, int>
#define st first
#define nd second
#define sp " "
#define modulo 1000000007
#define N 100005
#define int long long
int mm(pii r)
{
return (r.st + r.nd + 1) / 2;
}
int m(pii l)
{
return (l.st + l.nd) / 2;
}
int ask(int x)
{
cout<<"? "<<x<<endl;
int res;
cin>>res;
return res;
}
int32_t main()
{
int t = 1;
//cin>>t;
while(t--)
{
int n;
cin>>n;
int mid = (n + 1) / 2;
pii l = {1, mid};
pii r = {mid + 1, n};
int res = ask(m(l));
res = ask(mm(r));
int ll = 0, rr = n;
int steps = 2;
int vl = 1, vr = n;
while(l.st <= l.nd && r.st <= r.nd && vl < vr)
{
if (res == 1)
{
ll = m(l), rr = mm(r);
vr = mm(r) - m(l);
l = {m(l) + 1, l.nd};
}
else
{
vl = mm(r) - m(l) + 1;
l = {l.st, m(l) - 1};
}
//cout<<vl<<sp<<vr<<endl;
//cout<<l.st<<sp<<l.nd<<endl;
//cout<<r.st<<sp<<r.nd<<endl;
if (l.st <= l.nd && vl < vr)
{
if (steps == 64) return 1;
res = ask(m(l));
steps++;
if (res == 1)
{
ll = m(l), rr = mm(r);
vr = min(vr, mm(r) - m(l));
r = {r.st, mm(r) - 1};
}
else
{
vl = max(vl, mm(r) - m(l) + 1);
r = {mm(r) + 1, r.nd};
}
if (r.st <= r.nd && vl < vr)
{
if (steps == 64) return 1;
res = ask(mm(r));
steps++;
}
}
//cout<<l.st<<sp<<l.nd<<endl;
//cout<<r.st<<sp<<r.nd<<endl;
}
int ans = rr - ll;
if (vl == vr) ans = vl;
cout<<"= "<<ans<<endl;
}
cerr<<"time taken : "<<(float)clock() / CLOCKS_PER_SEC<<" seconds\n";
}
