#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  int l = 1, r = 1'000'001;
  int prv = 0;
  cout << "? 0" << endl;
  while (r - l > 1) {
    int mid = (l + r) / 2;
    int cur = 2 * mid - prv - 1;
    cout << "? " << cur << endl;
    int res;
    cin >> res;
    (res == (cur >= prv) ? l : r) = mid;
    prv = cur;
  }
  cout << "! " << l << endl;
  return 0;
}