#include <bits/stdc++.h>
using namespace std;
int n;
string unu, doi;
int query(int x1, int y1, int x2, int y2) {
  string rez;
  cout << "? " << x1 << ' ' << y1 << ' ' << x2 << ' ' << y2 << "\n";
  cout.flush();
  cin >> rez;
  if (rez == "YES")
    return 1;
  else
    return 0;
}
int main() {
  int i, x, y;
  cin >> n;
  x = 1;
  y = 1;
  for (i = 1; i < n; i++) {
    if (query(x + 1, y, n, n)) {
      x++;
      unu.push_back('D');
    } else {
      y++;
      unu.push_back('R');
    }
  }
  x = n;
  y = n;
  for (i = 1; i < n; i++) {
    if (query(1, 1, x, y - 1)) {
      y--;
      doi.push_back('R');
    } else {
      x--;
      doi.push_back('D');
    }
  }
  cout << "! ";
  cout << unu;
  for (int i = doi.size() - 1; i >= 0; i--) cout << doi[i];
  cout.flush();
  return 0;
}
