#include <bits/stdc++.h>
using namespace std;
bool request(int r1, int r2, int c1, int c2) {
  string ans;
  cout << "? " << r1 << ' ' << r2 << ' ' << c1 << ' ' << c2 << endl;
  cin >> ans;
  assert(ans != "BAD");
  return (ans == "YES");
}
int main() {
  cin.sync_with_stdio(0);
  cout.sync_with_stdio(0);
  int n;
  cin >> n;
  char s[4100];
  int c1 = 1;
  int r1 = 1;
  int r2 = n;
  int c2 = n;
  for (int i = 0; i < n - 1; i++) {
    if (request(r1, c1 + 1, n, n)) {
      s[i] = 'R';
      c1++;
    } else {
      s[i] = 'D';
      r1++;
    }
  }
  for (int i = 2 * n - 2; i-- > n - 1;) {
    if (s[i - n + 1] == 'R') {
      c1--;
    } else {
      r1--;
    }
    if (request(r1, c1, r2 - 1, c2)) {
      s[i] = 'D';
      r2--;
    } else {
      s[i] = 'R';
      c2--;
    }
  }
  printf("! %s", s);
  cout << endl;
  return 0;
}
