#include <bits/stdc++.h>
using namespace std;
#pragma optimize("O3")
const int N = 100005;
long long arr[N];
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long n;
  cin >> n;
  string ans = "";
  long long x = 1, y = 1;
  if (n == 1) {
    cout << "! " << endl;
    return 0;
  }
  while (abs(x - n) + abs(y - n) >= n) {
    if (y + 1 <= n) {
      cout << "? " << x << ' ' << y + 1 << ' ' << n << ' ' << n << endl;
      fflush(stdout);
      string s;
      cin >> s;
      assert(s != "BAD");
      if (s == "YES") {
        ans += "R";
        y++;
      } else {
        x++;
        ans += "D";
      }
    } else {
      x++;
      ans += "D";
    }
  }
  x = n, y = n;
  string ans1 = "";
  while (x - 1 + y - 1 >= n) {
    if (x - 1 >= 1) {
      cout << "? " << 1 << ' ' << 1 << ' ' << x - 1 << ' ' << y << endl;
      fflush(stdout);
      string s;
      cin >> s;
      assert(s != "BAD");
      if (s == "YES") {
        ans1 += "D";
        x--;
      } else {
        y--;
        ans1 += "R";
      }
    } else {
      y--;
      ans1 += "D";
    }
  }
  reverse(ans1.begin(), ans1.end());
  cout << "! " << ans + ans1 << endl;
  fflush(stdout);
  return 0;
}
