#include <bits/stdc++.h>
using namespace std;
int n;
char s[10], rlt[505 << 1];
bool query(int r1, int c1, int r2, int c2) {
  printf("? %d %d %d %d\n", r1, c1, r2, c2);
  fflush(stdout);
  scanf("%s", s);
  return s[0] == 'Y';
}
int main() {
  scanf("%d", &n);
  int r = 1, c = 1, p = 0;
  while (r + c <= n) {
    if (query(r + 1, c, n, n))
      r++, rlt[p++] = 'D';
    else
      c++, rlt[p++] = 'R';
  }
  r = n, c = n, p = 2 * n - 2;
  while (r + c > n + 1) {
    if (query(1, 1, r, c - 1))
      c--, rlt[--p] = 'R';
    else
      r--, rlt[--p] = 'D';
  }
  printf("! %s\n", rlt);
  return 0;
}
