Counting Single-Letter Substrings

Given a string s, count the total number of substrings that contain at most one distinct letter. A substring is a contiguous sequence of characters within the string.

The idea is to group consecutive identical characters and then count the substrings within each group using the formula:

\(\frac{n(n+1)}{2}\)

where \(n\) is the length of a group of identical characters.

For example, given the string "aaabb":

• The group "aaa" has \(n=3\) and contributes \(\frac{3*4}{2} = 6\) substrings.
• The group "bb" has \(n=2\) and contributes \(\frac{2*3}{2} = 3\) substrings.

The total is 6 + 3 = 9.

inputFormat

The input consists of a single line containing the string s (which may include only lowercase letters).

Note: the string s can be empty, in which case the output should be 0.

outputFormat

Output a single integer representing the total number of substrings of s that contain at most one distinct letter.

## sample

aaabb

9