#include <bits/stdc++.h>
using namespace std;
bool query(int x1, int y1, int x2, int y2) {
  cout << "? " << x1 << " " << y1 << " " << x2 << " " << y2 << endl;
  string ans;
  cin >> ans;
  if (ans == "BAD") return 228;
  return ans == "YES";
}
int main() {
  int n, x, y, ax, ay;
  string l = "", r = "";
  cin >> n;
  ax = ay = n;
  x = y = 1;
  for (int i = 1; i < n; i++) {
    if (query(x + 1, y, n, n)) {
      x++;
      ax--;
      l += "D";
    } else {
      y++;
      ay--;
      l += "R";
    }
  }
  x = y = n;
  for (int i = 1; i < n; i++) {
    if (query(1, 1, x, y - 1)) {
      y--;
      r += "R";
    } else {
      x--;
      r += "D";
    }
  }
  reverse(r.begin(), r.end());
  cout << "! " << l + r << endl;
  return 0;
}
