#include <bits/stdc++.h>
using namespace std;
string s, r, t;
int q(int a, int b, int c, int d) {
  cout << "? " << a << " " << b << " " << c << " " << d << endl;
  cin >> s;
  return s == "YES";
}
int main() {
  int i, n, x, y;
  cin >> n;
  x = 1, y = 1;
  for (i = 1; i < n; i++) {
    if (q(x + 1, y, n, n))
      x++, r += "D";
    else
      y++, r += "R";
  }
  x = n, y = n;
  for (i = 1; i < n; i++) {
    if (q(1, 1, x, y - 1))
      y--, t = "R" + t;
    else
      x--, t = "D" + t;
  }
  cout << "! " << r << t;
}
