Two strings are given, find the length of longest common substring.

Write a function `solve`

that have the following parameter(s):

1.) *first string*

2.) *second string*

**Example**

Input:

`s1 = DASH`

`s2 = DAB`

Output:

`2`

**Explanation**

'DA' is the longest common substring.

**Constraints**

• The length of string will be greater than or equal to 1 and less than or equal to 1000