#include <bits/stdc++.h>
using namespace std;
inline void solve();
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  solve();
}
string abc = "abcdefghijklmnopqrstuvwxyz";
string ABC = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
string digits = "0123456789";
long long dist(long long a, long long b, long long c, long long d) {
  return abs(c - a) + abs(c - b);
}
void solve() {
  long long n;
  cin >> n;
  string ans1, ans2, ans;
  long long x1 = 1, y1 = 1, x2, y2;
  x2 = y2 = n;
  while (ans1.size() < n - 1) {
    cout << "? " << x1 + 1 << ' ' << y1 << ' ' << x2 << ' ' << y2 << endl;
    cin >> ans;
    if (ans == "YES") {
      x1++;
      ans1 += 'D';
    } else {
      y1++;
      ans1 += 'R';
    }
  }
  long long j = ans1.size() - 1;
  while (ans2.size() < n - 1) {
    if (ans1[j] == 'D') {
      x1--;
    } else {
      y1--;
    }
    j--;
    cout << "? " << x1 << ' ' << y1 << ' ' << x2 << ' ' << y2 - 1 << endl;
    cin >> ans;
    if (ans == "YES") {
      y2--;
      ans2 += 'R';
    } else {
      x2--;
      ans2 += 'D';
    }
  }
  reverse(ans2.begin(), ans2.end());
  cout << "! " << ans1 << ans2 << endl;
}
