Counting Substrings with Specific Boundary Character

Given a string s and a character c, your task is to count the number of substrings of s that start and end with c. A substring is any contiguous sequence of characters within the string. If the character c occurs n times in the string, then the total number of valid substrings is given by the formula: \(\frac{n(n+1)}{2}\). This problem requires efficient string processing and combinatorial counting.

inputFormat

The input consists of two lines:

• The first line contains the string s.
• The second line contains a single character c.

outputFormat

Output a single integer representing the number of substrings in s that begin and end with the character c.

abcabc
a

3