#include <bits/stdc++.h>
using ll = long long;

void charming() {
  int n; std::cin >> n;
  
  auto send = [](int x) -> int {
    std::cout << "? " << x << std::endl;
    std::cout.flush();
    int ret; std::cin >> ret;
    return ret;
  };

  auto answer = [](int x) -> void {
    std::cout << "! " << x << std::endl;
    std::cout.flush();
  };

  int l = 1, r = n, k = 1, diff = 0;
  while (l <= r) {
    int mid = l + r >> 1;
    int ret = send(mid);
    if (ret == diff) {k = mid; break;}
    else if (ret > diff) l = mid + 1;
    else r = mid - 1;
    diff = ret;
  }
  
  answer(k);
}

signed main() {
  std::ios_base::sync_with_stdio(false);
  std::cin.tie(NULL);
  std::cout.tie(NULL);
  charming();
  return 0;
}