#include <bits/stdc++.h>
using namespace std;
char ret[2005];
int cnt;
int main() {
  int n;
  cin >> n;
  int nowx = 1;
  int nowy = 1;
  for (int i = 0; i < n - 1; i++) {
    printf("? %d %d %d %d\n", nowx, nowy + 1, n, n);
    fflush(stdout);
    string ans;
    cin >> ans;
    if (ans == "YES") {
      ret[i] = 'R';
      nowy++;
    } else {
      ret[i] = 'D';
      nowx++;
    }
  }
  int tempx = nowx;
  int tempy = nowy;
  nowy = n;
  nowx = n;
  for (int i = 0; i < n - 1; i++) {
    printf("? %d %d %d %d\n", 1, 1, nowx - 1, nowy);
    fflush(stdout);
    string ans;
    cin >> ans;
    if (ans == "YES") {
      ret[2 * n - 3 - i] = 'D';
      nowx--;
    } else {
      ret[2 * n - 3 - i] = 'R';
      nowy--;
    }
  }
  printf("! %s\n", ret);
  return 0;
}
