#include <bits/stdc++.h>
using namespace std;
inline bool ask(int x1, int y1, int x2, int y2) {
  cout << "? " << x1 << " " << y1 << " " << x2 << " " << y2 << "\n";
  fflush(stdout);
  string s;
  cin >> s;
  return s == "YES";
}
int main() {
  int n, x = 1, y = 1;
  cin >> n;
  string ans;
  while (x + y != n + 1) {
    if (ask(x + 1, y, n, n)) {
      ans += 'D';
      x++;
    } else {
      ans += 'R';
      y++;
    }
  }
  x = n, y = n;
  string anss;
  while (x + y != n + 1) {
    if (ask(1, 1, x, y - 1)) {
      anss += 'R';
      y--;
    } else {
      anss += 'D';
      x--;
    }
  }
  reverse(anss.begin(), anss.end());
  cout << "! " << ans << anss;
  fflush(stdout);
}
