Lockpicking Chef

Chef bought a new digital lock, but is quite suspicious of its actual strength in keeping out pesky thieves. So, he wants to find out how quickly he can open the lock. The digital lock works as follows: - On its screen, there is a string of digits $S$ of length $N$. - There is also a secret code $K$ of length $M$ ($1 \leq M \leq 10$), which acts as the key to the lock. The lock will open if $K$