#include <bits/stdc++.h>
using namespace std;

using ll = __int128_t;

#define int long long

using ii = pair<int, int>;

// #define endl '\n'

const int ms = 505;

int query(int x) {
  cout << "? " << x << endl;
  int y;
  cin >> y;
  return y;
}

void go(int i){
  cout << "! " << i << endl;
  exit(0); 
}

void solve() {
  int n;
  cin >> n;
  for(int i = 1; i <= min(n, 20ll); i++) {
    int ans = query(i);
    if(ans != i) {
      go(i);
    }
  }
  int num = 20;
  int lo = 21, hi = n;
  while(lo != hi) {
    int mi = (lo+hi)/2;
    int k = query(mi);
    if(k == num) {
      lo = mi;
      hi = mi;
    } else if(k > num) {
      lo = mi+1;
    } else {
      hi = mi - 1;
    }
  }
  go(lo);
}

int32_t main() {
    cin.tie(0); ios::sync_with_stdio(0);
    cout << fixed << setprecision(9);
    int testes = 1;
    // cin >> testes;
    int test = 0;

    while(testes--) {
      // cout << "Case #" << (++test) << ": ";
        solve();
    }
}