#pragma GCC optimize(3)
#include <bits/stdc++.h>

#define f(i, n, m) for (long long i = n; i <= m; ++i)
#define unf(i, n, m) for (long long i = n; i >= m; --i)
#define kong NULL
#define debug cout << "sss" << endl;

using ll = long long;
using ull = unsigned long long;
using point_t = double; // 计算几何的默认类型

const double e = exp(1.0);
const double pi = acos(-1.0);
constexpr ll inf = 0x3f3f3f3f3f3f3f3f;
constexpr ll maxx = 0x3f3f3f3f3f3f3f3f;
constexpr ll minn = 0xc0c0c0c0c0c0c0c0;

// #define endl '\n'
constexpr char blank = ' ';
constexpr ll mod = (ll)998244353;
constexpr size_t N = (size_t)1e6 + 6;

#ifdef _DEBUG
#define Crash(...) (__debugbreak(), 0)
#define Debug(...) (__debugbreak(), 0)
#else
#define Crash(...) (exit(-1), 0)
#define Debug(...) ((void)0)
#endif // _DEBUG

#define ensure(expression) (void)(!!(expression) || Crash())

inline void setaccuracy(const std::streamsize &accuracy)
{
  std::cout << std::fixed << std::setprecision(accuracy);
}

#define int long long
using namespace std;


void solve()
{
  int n;
  cin>>n;
  int l=1,r=n;
  int jue=0;
  f(i,1,min(n,(int)20)){
    cout<<"? "<<i<<endl;
    int a;
    cin>>a;
    if(a==jue){
      cout<<"! "<<i<<endl;
      return;
    }
    jue=a;
  }
  l=21;
  while(l<=r){
    int mid=l+r>>1;
    cout<<"? "<<mid<<endl;
    int a;
    cin>>a;
    if(a>jue){
      l=mid+1;
    }
    else if(a<jue){
      r=mid-1;
    }
    else {
      cout<<"! "<<mid<<endl;
      return;
    }

  }


  // std::cout<< minn<<endl;
}

signed main()
{
  // ios::sync_with_stdio(false);
  // std::cin.tie(nullptr);
  // std::cout.tie(nullptr);
  int T = 1;
  // cin >> T;
  // scanf(" %d", &T);
  // std::cin >> T;
  // for (int q = 1; q <= T; q++) {
  // while (T--) {
  solve();
  // }

  return 0;
}