Minimum Changes to Achieve K Distinct Characters

Given a string s and an integer k, determine the minimum number of character modifications required so that the string contains at least k distinct characters. In other words, if \( \lvert U \rvert \) denotes the number of unique characters in s, then the answer is given by

[ \max(0, k - \lvert U \rvert ) ]

You may assume that k is less than or equal to the length of s.

inputFormat

The input consists of two lines:

• The first line contains a single integer k.
• The second line contains the string s.

outputFormat

Output a single integer representing the minimum number of changes required so that s contains at least k distinct characters.

## sample

5
aaabbcc

2

</p>