#include <bits/stdc++.h>
using namespace std;
int n, x, y, xm, ym;
string p, ans, t;
void ask(int x1, int y1, int x2, int y2) {
  cout << "? " << x1 << ' ' << y1 << ' ' << x2 << ' ' << y2 << endl;
  cin >> p;
}
int main() {
  cin >> n;
  x = y = n;
  while ((x - 1) + (y - 1) > n - 1 && t.size() < n - 1) {
    ask(1, 1, x - 1, y);
    if (p == "YES")
      x--, t += 'D';
    else
      y--, t += 'R';
  }
  reverse(t.begin(), t.end());
  x = y = 1;
  while ((n - x) + (n - y) > n - 1 && ans.size() < n - 1) {
    ask(x, y + 1, n, n);
    if (p == "YES")
      y++, ans += 'R';
    else
      x++, ans += 'D';
  }
  cout << "! " << ans + t << endl;
  return 0;
}
