思考题 Times

A shadow pokemon!

Recently the famous game Pokemon SwordString was released. XGN, one of the biggest fan of Pokemon, decided to have a try.
In each battle, your Pokemon can be seen as a string A and the enemy can be seen as a string B. One can make a critical hit if B is a substring of A.
XGN can weaken the foe first. He can remove a character from B each turn.
What's the minimum turn of weakening to make a critical hit?

Sample

Example 1

In
A=eevee
B=eveee
Output
1
Explain
Remove the last 'e' in B and B will be a substring of A

Example 2

In
A=pikachu
B=reshiram
Output
7
Explain

Screenshot from Pokemon Essentials

Constriants

Subtask 1(20%):|A|,|B|<=20
Subtask 2(40%):|A|,|B|<=1000
Subtask 3(40%):|A|,|B|<=100000
Is it really good to release 2 simple questions at once?