You’re standing by the statue of Viggo Hørup, the politician.
Viggo is in on the idea regarding preserving The Royal Garden, and he is eager to sign the document.
Sadly, Viggo is unable to remember which stamp is used for the preservation of gardens.
Luckily, he has made a note that can help get him going:
17, 31, 21, 1, 13, 11, 10, 43, 43
Enter the answer here: (x)