#include <bits/stdc++.h>
using namespace std;
const int max_N = 510;
int ask(int r1, int c1, int r2, int c2);
int main() {
  int N;
  cin >> N;
  string ans;
  int x = N, y = N;
  for (int i = 1; i < N; ++i) {
    if (ask(1, 1, x - 1, y)) {
      ans += 'D';
      --x;
    } else {
      ans += 'R';
      --y;
    }
  }
  x = 1, y = 1;
  string phase2;
  for (int i = 1; i < N; ++i) {
    if (ask(x, y + 1, N, N)) {
      phase2 += 'R';
      ++y;
    } else {
      phase2 += 'D';
      ++x;
    }
  }
  reverse(ans.begin(), ans.end());
  cout << "! " << phase2 + ans << endl;
}
int ask(int r1, int c1, int r2, int c2) {
  cout << "? " << r1 << ' ' << c1 << ' ' << r2 << ' ' << c2 << ' ' << endl;
  string ret;
  cin >> ret;
  if (ret == "BAD") {
    exit(0);
  }
  return (ret == "YES");
}
