#include <bits/stdc++.h>
using namespace std;
bool ask(int a, int b, int c, int d) {
  cout << "? " << a << " " << b << " " << c << " " << d << endl;
  fflush(stdout);
  string response;
  cin >> response;
  if (response == "BAD") {
    exit(0);
  } else if (response == "YES")
    return true;
  else
    return false;
}
int main() {
  int n;
  cin >> n;
  int x = 1, y = 1;
  string ans1 = "", ans2 = "";
  for (int i = 0; i < n - 1; ++i) {
    if (ask(x + 1, y, n, n)) {
      x++;
      ans1.push_back('D');
    } else {
      y++;
      ans1.push_back('R');
    }
  }
  x = n, y = n;
  for (int i = 0; i < n - 1; ++i) {
    if (ask(1, 1, x, y - 1)) {
      y--;
      ans2.push_back('R');
    } else {
      x--;
      ans2.push_back('D');
    }
  }
  reverse((ans2).begin(), (ans2).end());
  string finalans = ans1 + ans2;
  cout << "! " << finalans << endl;
  fflush(stdout);
  return 0;
}
