#include <bits/stdc++.h>
const int N = 505;
using namespace std;
bool query(int x, int y, int z, int t) {
  string s;
  cout << "? " << x << " " << y << " " << z << " " << t << endl;
  cin >> s;
  if (s == "YES") return true;
  return false;
}
char s[N];
int n;
int main() {
  cin >> n;
  int x = 1, y = 1;
  for (int i = 0; i < n - 1; i++) {
    if (query(x, y + 1, n, n))
      y++, s[i] = 'R';
    else
      x++, s[i] = 'D';
  }
  x = n;
  y = n;
  for (int i = 2 * n - 3; i >= n - 1; i--) {
    if (query(1, 1, x - 1, y))
      x--, s[i] = 'D';
    else
      y--, s[i] = 'R';
  }
  cout << "! " << s;
}
