#include <bits/stdc++.h> using namespace std; long long i, j, l, r, mid, p, q, k, t, n, m, a, b, c, d, ans, cnt, res; const long long mod = 999993143, mod2 = 999993469; string s; bool check; int main(){ ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0); cin >> n; a = 1; b = n; c = n / 2; l = 0; r = c - 1; t = -1; while (l <= r && a < b){ mid = (l + r) / 2; if (n % 2 == 1 && mid == c - 1){ cout << "? " << n << endl; cin >> d; if (t != -1){ if (d == 0){ a = max(a, abs(n - t) + 1); } else{ b = min(b, abs(n - t)); } } t = n; cout << "? " << 1 << endl; cin >> d; if (t != -1){ if (d == 0){ a = max(a, abs(1 - t) + 1); } else{ b = min(b, abs(1 - t)); } } t = 1; cout << "? " << n - 1 << endl; cin >> d; if (t != -1){ if (d == 0){ a = max(a, abs((n - 1) - t) + 1); } else{ b = min(b, abs((n - 1) - t)); } } break; } else{ cout << "? " << c - mid << endl; cin >> d; if (t != -1){ if (d == 0){ a = max(a, abs((c - mid) - t) + 1); } else{ b = min(b, abs((c - mid) - t)); } } t = c - mid; cout << "? " << c + mid + 1 << endl; cin >> d; if (t != -1){ if (d == 0){ a = max(a, abs((c + mid + 1) - t) + 1); l = mid + 1; } else{ b = min(b, abs((c + mid + 1) - t)); r = mid - 1; } } t = c + mid + 1; } } cout << "= " << a << endl; // cout << "= " << b << endl; }