#include <bits/stdc++.h>
using namespace std;
int main() {
long long n;
cin >> n;
if (n == 1 || n > 1000) {
cout << "= " << n;
return 0;
}
int x = sqrt(n), y = 1, cnt = 0;
for (int i = x / 2 + 1; i <= x; i++) {
int num = i;
while (num + x <= n) num += x;
if (n - num >= i - 1 && (n - num) - (i - 1) <= 1) {
y = i;
break;
}
}
int save[55];
while (y <= n) {
save[++cnt] = y;
y += x;
}
int l = 1, r = cnt, curr = 0, border = n, prev = save[cnt];
cout << "? " << save[cnt] << endl;
int ngaos; cin >> ngaos;
while (l < r) {
if (!curr) cout << "? " << save[l] << endl;
else cout << "? " << save[r] << endl;
int res;
cin >> res;
if (res == 1) {
if (!curr) {
border = abs(prev - save[l]);
prev = save[l]; r--;
}
else {
border = abs(prev - save[r]);
prev = save[r]; l++;
}
}
else {
int P = save[l], Q = save[r], turn = 1 - curr;
while (P != 1 || Q != n) {
if (turn) cout << "? " << ++Q << endl;
else cout << "? " << --P << endl;
turn = 1 - turn;
cin >> res;
if (res == 1) {
cout << "= " << Q - P;
return 0;
}
}
cout << "= " << border;
return 0;
}
curr = 1 - curr;
}
int turn = 0, bim = save[l];
for (int i = border - 1; i >= 1; i--) {
if (!turn) bim += i;
else bim -= i;
turn = 1 - turn;
cout << "? " << bim << endl;
int res; cin >> res;
if (!res) {
cout << "= " << i + 1;
return 0;
}
}
cout << "= " << 1;
return 0;
}
