#include <bits/stdc++.h>
using namespace std;
long long int n;
long long int ask(long long int r1, long long int c1, long long int r2,
                  long long int c2) {
  if (r1 < 1 || r1 > n) return 0;
  if (r2 < 1 || r2 > n) return 0;
  if (c1 < 1 || c1 > n) return 0;
  if (c1 < 1 || c2 > n) return 0;
  cout << "? " << r1 << " " << c1 << " " << r2 << " " << c2 << '\n';
  fflush(stdout);
  string s;
  cin >> s;
  return s == "YES";
}
int main() {
  int TESTS = 1;
  while (TESTS--) {
    cin >> n;
    long long int cr = 1, cc = 1;
    string s;
    while (cr + cc != n + 1) {
      if (ask(cr + 1, cc, n, n)) {
        s += 'D';
        cr++;
      } else {
        s += 'R';
        cc++;
      }
    }
    string t;
    cr = n, cc = n;
    while (cr + cc != n + 1) {
      if (ask(1, 1, cr, cc - 1)) {
        t += 'R';
        cc--;
      } else {
        t += 'D';
        cr--;
      }
    }
    reverse((t).begin(), (t).end());
    s += t;
    cout << "! " << s << '\n';
    fflush(stdout);
  }
  return 0;
}
