#include <bits/stdc++.h>
using namespace std;
const int INF = (int)1E9;
int n;
bool query(int x1, int y1, int x2, int y2) {
  printf("? %d %d %d %d\n", x1, y1, x2, y2);
  fflush(stdout);
  string res;
  cin >> res;
  return res == "YES";
}
int main() {
  int x = 1, y = 1;
  cin >> n;
  string ans = "", rans = "";
  for (int i = (0); i < (n - 1); i++) {
    if (x + 1 <= n && query(x + 1, y, n, n)) {
      x++;
      ans += "D";
    } else {
      y++;
      ans += "R";
    }
  }
  x = y = n;
  for (int i = (0); i < (n - 1); i++) {
    if (y - 1 >= 1 && query(1, 1, x, y - 1)) {
      y--;
      rans += "R";
    } else {
      x--;
      rans += "D";
    }
  }
  reverse(rans.begin(), rans.end());
  cout << "! " << ans << rans << endl;
  return 0;
}
