A string is said to be a child of a another string if it can be formed by deleting 0 or more characters from the other string. Letters cannot be rearranged. Given two strings of equal length, what's the longest string that can be constructed such that it is a child of both?

**Example**

These strings have two children with maximum length 3, `ABC`

and `ABD`

. They can be formed by eliminating either the `D`

or `C`

from both strings. Return .

**Function Description**

Complete the *commonChild* function in the editor below.

commonChild has the following parameter(s):

*string s1:*a string*string s2:*another string

**Returns**

*int:*the length of the longest string which is a common child of the input strings

**Input Format**

There are two lines, each with a string, and .

**Constraints**

- where means "the length of "
- All characters are upper case in the range ascii[A-Z].

**Sample Input**

```
HARRY
SALLY
```

**Sample Output**

```
2
```

**Explanation**

The longest string that can be formed by deleting zero or more characters from and is , whose length is 2.

**Sample Input 1**

```
AA
BB
```

**Sample Output 1**

```
0
```

**Explanation 1**

and have no characters in common and hence the output is 0.

**Sample Input 2**

```
SHINCHAN
NOHARAAA
```

**Sample Output 2**

```
3
```

**Explanation 2**

The longest string that can be formed between and while maintaining the order is .

**Sample Input 3**

```
ABCDEF
FBDAMN
```

**Sample Output 3**

```
2
```

**Explanation 3**

is the longest child of the given strings.