#include <bits/stdc++.h>
using namespace std;
template <class T1, class T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) {
  os << "{" << p.first << "," << p.second << "}";
  return os;
}
const int N = 3e5 + 5;
const int oo = 1e9 + 7;
int n;
int ask(int r1, int c1, int r2, int c2) {
  assert(r2 - r1 + c2 - c1 >= n - 1);
  cout << "? " << r1 << " " << c1 << " " << r2 << " " << c2 << endl;
  string s;
  cin >> s;
  assert(s != "BAD");
  return s == "YES";
}
int32_t main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cout.tie(nullptr);
  cin >> n;
  string ans = "";
  pair<int, int> now = {1, 1};
  for (int i = 1; i <= (n - 1); i++) {
    if (now.first + 1 <= n and ask(now.first + 1, now.second, n, n))
      ans += "D", now.first++;
    else
      ans += "R", now.second++;
  }
  string ans2 = "";
  pair<int, int> now2 = {n, n};
  for (int i = 1; i <= (n - 1); i++) {
    if (now2.second - 1 >= 1 and ask(1, 1, now2.first, now2.second - 1))
      ans2 = "R" + ans2, now2.second--;
    else
      ans2 = "D" + ans2, now2.first--;
  }
  cout << "! " << ans + ans2 << "\n";
}
