#include <bits/stdc++.h>
template <class T>
inline bool chmax(T& a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T>
inline bool chmin(T& a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
constexpr long long MAX = 5100000;
constexpr long long INF = 1LL << 60;
constexpr int inf = 1000000007;
const long double PI = acos((long double)(-1));
using namespace std;
bool ask(int h1, int w1, int h2, int w2) {
  cout << "? " << h1 << " " << w1 << " " << h2 << " " << w2 << endl;
  string s;
  cin >> s;
  return s == "YES";
}
int main() {
  int n;
  cin >> n;
  string s, t;
  {
    int curh = 1;
    int curw = 1;
    while (curh + curw < n + 1) {
      if (curh < n and ask(curh + 1, curw, n, n)) {
        s += 'D';
        curh += 1;
      } else {
        s += 'R';
        curw += 1;
      }
    }
  }
  {
    {
      int curh = n;
      int curw = n;
      while (curh + curw > n + 1) {
        if (curw > 1 and ask(1, 1, curh, curw - 1)) {
          t += 'R';
          curw -= 1;
        } else {
          t += 'D';
          curh -= 1;
        }
      }
    }
  }
  reverse(t.begin(), t.end());
  s += t;
  cout << "! " << s << endl;
  return 0;
}
