#include <bits/stdc++.h>
using namespace std;
bool can(int x, int y, int a, int b) {
  cout << "? " << x << " " << y << " " << a << " " << b << endl;
  string ans;
  cin >> ans;
  if (ans == "BAD") exit(0);
  return ans == "YES";
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n;
  cin >> n;
  int x = 1, y = 1;
  string ord1(n - 1, ' '), ord2(n - 1, ' ');
  int i = 0;
  while (i < n - 1) {
    if (can(x + 1, y, n, n)) {
      ++x;
      ord1[i] = 'D';
    } else {
      ord1[i] = 'R';
      ++y;
    }
    ++i;
  }
  x = n;
  y = n;
  i = 0;
  while (i < n - 1) {
    if (can(1, 1, x, y - 1)) {
      ord2[i] = 'R';
      --y;
    } else {
      --x;
      ord2[i] = 'D';
    }
    ++i;
  }
  reverse(ord2.begin(), ord2.end());
  cout << "! " << ord1 << ord2 << endl;
}
