#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; long double cur; map <long long, long long> mp; int main(){ ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0); cin >> n; if (n > 64){ l = 1; r = n; a = 1; b = n; res = n / 3; mp[res] = 1; cout << "? " << res << endl; cin >> d; cnt = 0; t = res; while (l < r){ mid = (l + r) / 2; if (cnt % 2 == 0){ res += mid; } else{ res -= mid; } check = false; if (t == 1){ if (mp[n] == 0){ res = n; check = true; } } if (t == n){ if (mp[1] == 0){ res = 1; check = true; } } if (check == false){ if (mp[res] == 1 || res <= 0 || res > n){ res -= 1; if (mp[res] == 1 || res <= 0 || res > n){ res += 2; if (mp[res] == 1 || res <= 0 || res > n){ res -= 3; if (mp[res] == 1 || res <= 0 || res > n){ res += 4; if (mp[res] == 1 || res <= 0 || res > n){ res -= 5; if (mp[res] == 1 || res <= 0 || res > n){ res += 6; if (mp[res] == 1 || res <= 0 || res > n){ break; } } } } } } } } mp[res] = 1; cout << "? " << res << endl; cin >> d; if (d == 0){ a = max(a, abs(t - res) + 1); l = a; } else{ b = min(b, abs(t - res)); r = b; } c = a; d = b; a = min(c, d); b = max(c, d); cnt += 1; t = res; } cout << "= " << a << endl; } else{ ans = 0; l = 2; r = n; cout << "? 1" << endl; cin >> d; for (i = 2; i <= n; i += 1){ if (i % 2 == 1){ cout << "? " << l << endl; l += 1; } else{ cout << "? " << r << endl; r -= 1; } cin >> d; if (d == 0){ break; } else{ ans += 1; } } cout << "= " << n - ans << endl; } }