#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
const int N = 505;
int n, c;
char r[2 * N];
int q(int x, int y, int z, int w) {
  printf("? %d %d %d %d\n", x, y, z, w);
  fflush(stdout);
  char res[5];
  scanf("%s", res);
  return res[0] == 'Y';
}
int main() {
  scanf("%d", &n);
  for (int a = 1, b = 1; a + b < n + 1;) {
    if (q(a, b + 1, n, n)) {
      r[c++] = 'R';
      b++;
    } else {
      r[c++] = 'D';
      a++;
    }
  }
  c = 2 * n - 3;
  for (int a = n, b = n; a + b > n + 1;) {
    if (q(1, 1, a - 1, b)) {
      r[c--] = 'D';
      a--;
    } else {
      r[c--] = 'R';
      b--;
    }
  }
  printf("! %s\n", r);
  fflush(stdout);
  return 0;
}
