#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("unroll-loops")
#pragma GCC optimize("Ofast")
#pragma GCC optimize("O3")
const long long inf = 4e18;
const int infi = 2e9;
long long i, j, n, m, k, qq = 0, fr, to, w, x, y, mod = 998244353;
char ch;
vector<pair<long long, long long> > a = {{1, 1}}, b = {{n, n}};
string second;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cin >> n;
  b = {{n, n}};
  x = n, y = n;
  for (int i = 0; i < n - 1; i++) {
    cout << "? 1 1 " << x << ' ' << y - 1 << endl;
    cin >> second;
    if (second == "YES")
      y--;
    else
      x--;
    b.push_back({x, y});
  }
  x = 1;
  y = 1;
  for (int i = 0; i < n - 1; i++) {
    cout << "? " << x + 1 << ' ' << y << ' ' << n << ' ' << n << endl;
    cin >> second;
    if (second == "YES")
      x++;
    else
      y++;
    a.push_back({x, y});
  }
  b.pop_back();
  reverse((b).begin(), (b).end());
  for (auto x : b) a.push_back(x);
  cout << "! ";
  for (int i = 1; i < a.size(); i++) {
    if (a[i].first == a[i - 1].first)
      cout << "R";
    else
      cout << "D";
  }
  cout << endl;
}
