#include <bits/stdc++.h>
using namespace std;
char amid[100010];
int main() {
  int n;
  cin >> n;
  string str;
  int len = 0;
  int cx = 1, cy = 1;
  for (int i = 1; i <= n - 1; i++) {
    cout << "? " << cx + 1 << " " << cy << " " << n << " " << n << '\n';
    fflush(stdout);
    cin >> str;
    if (str == "YES") {
      amid[cx + cy - 2] = 'D';
      cx++;
      continue;
    }
    amid[cx + cy - 2] = 'R';
    cy++;
  }
  cx = n, cy = n;
  for (int i = 1; i <= n - 1; i++) {
    cout << "? "
         << "1 1 " << cx << " " << cy - 1 << '\n';
    fflush(stdout);
    cin >> str;
    if (str == "YES") {
      amid[cx + cy - 3] = 'R';
      cy--;
      continue;
    }
    amid[cx + cy - 3] = 'D';
    cx--;
  }
  cout << "! ";
  fflush(stdout);
  for (int i = 0; i < 2 * n - 2; i++) {
    cout << amid[i];
    fflush(stdout);
  }
  cout << '\n';
  fflush(stdout);
  return 0;
}
