#include <bits/stdc++.h>
using namespace std;
const long long mod = 1e9 + 7;
const int MaxN = 1e6 + 5;
long long n, c;
void Inp()
{
cin >> n;
#ifdef cpismylifeOwO
cin >> c;
#endif // cpismylifeOwO
}
int quecnt;
long long cur;
set<long long> s;
bool Ask(long long k)
{
cout << "? " << k << "\n";
cout.flush();
#ifdef cpismylifeOwO
if (s.find(k) != s.end())
{
cout << "Rewrite\n";
}
s.insert(k);
long long pre = cur;
cur = k;
quecnt++;
cout << (abs(pre - k) >= c) << "\n";
cout.flush();
return (abs(pre - k) >= c);
#else
bool p;
cin >> p;
return p;
#endif // cpismylifeOwO
}
void Ans(long long k)
{
cout << "= " << k << "\n";
cout.flush();
#ifdef cpismylifeOwO
cout << (k == c) << "\n";
cout.flush();
#endif // cpismylifeOwO
}
void Exc()
{
cur = quecnt = 0;
long long curmi = 0, now = 0, lt = 1, rt = n - 1;
bool neg = true;
while (lt <= rt)
{
long long mid = (lt + rt) / 2;
if (neg)
{
now += mid;
neg = false;
}
else
{
now -= mid;
neg = true;
}
curmi = min(curmi, now);
lt = mid + 1;
}
curmi = 1 - curmi;
Ask(curmi);
neg = true;
long long l = 1, r = n - 1, mid, res = n;
while (l <= r)
{
mid = (l + r) / 2;
if (neg)
{
curmi += mid;
neg = false;
}
else
{
curmi -= mid;
neg = true;
}
if (Ask(curmi))
{
res = mid;
r = mid - 1;
}
else
{
l = mid + 1;
}
}
Ans(res);
}
int main()
{
//freopen("COLORS.INP", "r", stdin);
//freopen("COLORS.OUT", "w", stdout);
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
int test = 1;
//cin >> test;
for (int x = 1; x <= test; x++)
{
Inp();
Exc();
}
return 0;
}
