#include <bits/stdc++.h>
using namespace std;
const int NMAX = 1e5 + 4;
const int N = 5e5 + 5;
const long long IMAX = -2e18;
const long long MOD = 1e9 + 7;
const long double pi = 3.141592653589793238462643383;
template <class T>
using max_pq = priority_queue<T>;
template <class T>
using min_pq = priority_queue<T, vector<T>, greater<T>>;
long long x, y;
template <class T>
T gcd(T a, T b) {
  if (a == 0) {
    x = 0, y = 1;
    return b;
  }
  T gc = gcd(b % a, a);
  T temp;
  temp = x;
  x = y - (b / a) * temp;
  y = temp;
  return gc;
}
long long po(long long a, long long x, long long m) {
  if (x == 0) {
    return 1;
  }
  long long ans = 1;
  long long k = 1;
  while (k <= x) {
    if (x & k) {
      ans = ((ans * a) % m);
    }
    k <<= 1;
    a *= a;
    a %= m;
  }
  return ans;
}
vector<int> st;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int n;
  cin >> n;
  string a;
  string ans;
  int curx = 1, cury = 1;
  for (int i = int(1); i <= int(n - 1); i++) {
    cout << "? " << curx << " " << cury + 1 << " " << n << ' ' << n << endl;
    cin >> a;
    assert(a != "BAD");
    if (a == "YES") {
      ans.push_back('R');
      cury += 1;
    } else {
      ans.push_back('D');
      curx += 1;
    }
  }
  string ans1;
  curx = n;
  cury = n;
  for (int i = int(1); i <= int(n - 1); i++) {
    cout << "? 1 1 " << curx - 1 << " " << cury << endl;
    cin >> a;
    assert(a != "BAD");
    if (a == "YES") {
      ans1.push_back('D');
      curx -= 1;
    } else {
      ans1.push_back('R');
      cury -= 1;
    }
  }
  cout << "! ";
  for (int i = int(0); i <= int(n - 2); i++) cout << ans[i];
  for (int i = int(n - 2); i >= int(0); i--) cout << ans1[i];
  cout << endl;
  return 0;
}
