#include <bits/stdc++.h>
using namespace std;
int n;
int query(int r1, int c1, int r2, int c2) {
  cout << '?' << ' ' << r1 << ' ' << c1 << ' ' << r2 << ' ' << c2 << '\n';
  string res;
  cin >> res;
  return res == "YES";
}
int main() {
  ios_base::sync_with_stdio(false);
  cin >> n;
  int r = 1, c = 1;
  string fir, sec;
  for (int i = 1; i < n; ++i) {
    if (query(r, c + 1, n, n)) {
      fir += 'R';
      c++;
    } else {
      fir += 'D';
      r++;
    }
  }
  r = n, c = n;
  for (int i = 1; i < n; ++i) {
    if (query(1, 1, r - 1, c)) {
      sec += 'D';
      r--;
    } else {
      sec += 'R';
      c--;
    }
  }
  reverse(sec.begin(), sec.end());
  string res = fir + sec;
  cout << '!' << ' ' << res;
}
