#include <bits/stdc++.h>
using namespace std;
string to_string(string s) { return '"' + s + '"'; }
string to_string(const char* s) { return to_string((string)s); }
string to_string(bool b) { return (b ? "true" : "false"); }
template <typename A, typename B>
string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
template <typename A>
string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto& x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}
void debug_out() { cerr << '\n'; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}
bool can(int a, int b, int c, int d) {
  cout << "? " << a << " " << b << " " << c << " " << d << '\n';
  cout.flush();
  string s;
  cin >> s;
  assert(s[0] != 'B');
  return s == "YES";
}
void solve() {
  int n;
  cin >> n;
  vector<pair<int, int> > cur = {{1, 1}};
  int cx = 1;
  int cy = 1;
  for (int i = 1; i < n; i++) {
    if (can(cx + 1, cy, n, n)) {
      cx++;
    } else {
      cy++;
    }
    cur.push_back({cx, cy});
  }
  42;
  cx = n;
  cy = n;
  vector<pair<int, int> > cur2 = {{n, n}};
  for (int i = 1; i < n; i++) {
    if (can(cur[(int)cur.size() - 1 - i].first,
            cur[(int)cur.size() - 1 - i].second, cx, cy - 1)) {
      cy--;
    } else
      cx--;
    cur2.push_back({cx, cy});
  }
  cur2.pop_back();
  42;
  reverse((cur2).begin(), (cur2).end());
  for (auto i : cur2) cur.push_back(i);
  42;
  string s;
  for (int i = 1; i < (int)cur.size(); i++) {
    if (cur[i].second != cur[i - 1].second)
      s.push_back('R');
    else
      s.push_back('D');
  }
  cout << "! " << s << '\n';
  cout.flush();
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int t = 1;
  while (t--) {
    solve();
  }
  return 0;
}
