#include <bits/stdc++.h>
using namespace std;
int n;
vector<char> ans1, ans2;
bool ask(int r1, int c1, int r2, int c2) {
  cout << "? " << r1 << " " << c1 << " " << r2 << " " << c2 << "\n" << flush;
  string x;
  cin >> x;
  if (x == "YES") return 1;
  return 0;
}
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cin >> n;
  int curx = 1, cury = 1;
  while (n - curx + n - cury >= n) {
    bool tmp = ask(curx + 1, cury, n, n);
    if (tmp)
      ans1.push_back('D'), curx++;
    else
      ans1.push_back('R'), cury++;
  }
  int curx2 = n, cury2 = n;
  while (curx2 != curx || cury2 != cury) {
    bool tmp = ask(1, 1, curx2, cury2 - 1);
    if (tmp)
      ans2.push_back('R'), cury2--;
    else
      ans2.push_back('D'), curx2--;
  }
  reverse(ans2.begin(), ans2.end());
  cout << "! ";
  for (auto i : ans1) cout << i;
  for (auto i : ans2) cout << i;
  return 0;
}
