Alohomora

Hermione, Harry, and Ron are at the entrance of the locked door in the flying key room. Of course, they try the age-old spell "Alohomora," but the door won't open. To open the door, they must use the key to the lock. The lock consists of $n$ disks. Each disk shows a digit from $0$ to $9$. Currently, the $i^{\text{th}}$ disk shows digit $s_i$, making a string $s = s_1 s_2 \ldots s_n$. When a disk