Make a Periodic String

Sejun is a biologist, so he often works with DNA strings. One day, he became tired of looking at a long DNA string and wanted to express it in a simpler periodic form.

For a string of length $L$, a positive integer $P$ is a period length if, for every integer $i$ with $0 \le i \le L-P-1$, the character at position $i$ is the same as the character at position $i+P$. For example, CATCATC, CATCAT, ACTAC, and ACT all have period length $3$.

Given a DNA string, change as few characters as possible so that it becomes a periodic string whose period length is at most $M$. Find the minimum number of characters that must be changed.

The first line contains $M$. The value of $M$ is at most the length of the string.

The second line contains the DNA string. The string consists only of A, C, G, and T, and its length is at most $3000$.

Print the minimum number of characters that must be changed.