#include <bits/stdc++.h>
using namespace std;
const int maxn = 2e5 + 10;
const int mod = 1e9 + 7;
string str;
bool query(int r1, int c1, int r2, int c2) {
  cout << "? " << r1 << " " << c1 << " " << r2 << " " << c2 << endl;
  cout.flush();
  cin >> str;
  if (str == "YES")
    return 1;
  else
    return 0;
}
int main() {
  std::ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int n;
  cin >> n;
  vector<char> ans;
  int row = 1, col = 1;
  while (row + col < n + 1) {
    if (query(row + 1, col, n, n)) {
      ans.push_back('D');
      row++;
    } else {
      ans.push_back('R');
      col++;
    }
  }
  vector<char> rans;
  row = n, col = n;
  while (row + col > n + 1) {
    if (query(1, 1, row, col - 1)) {
      rans.push_back('R');
      col--;
    } else {
      rans.push_back('D');
      row--;
    }
  }
  cout << "! ";
  for (int i = 0; i < ans.size(); i++) cout << ans[i];
  for (int i = rans.size() - 1; i >= 0; i--) cout << rans[i];
  return 0;
}
