use std::io::{stdin, BufRead, BufReader};
fn main() {
let mut stdin = BufReader::new(stdin());
let mut cur_line = String::new();
stdin.read_line(&mut cur_line).unwrap();
let mut nums = cur_line
.split_whitespace()
.map(|s| s.parse::<usize>().unwrap());
let n = nums.next().unwrap();
let k = nums.next().unwrap();
cur_line.clear();
stdin.read_line(&mut cur_line).unwrap();
let v = cur_line.as_bytes();
let mut max_a = 0;
let mut max_b = 0;
let mut max_c = 0;
let mut x = 0;
let mut max_abc = 0;
let mut max_ab = 0;
let mut max_bc = 0;
let mut max_ca = 0;
for i in 0..n {
max_abc = (max_abc + 1).min(k);
match v[i] {
b'A' => {
max_a += 1;
max_ab += 1;
max_ca += 1;
}
b'B' => {
max_b += 1;
max_ab += 1;
max_bc += 1;
}
b'C' => {
max_c += 1;
max_bc += 1;
max_ca += 1;
}
_ => (),
}
if max_a > 0
&& max_b > 0
&& max_c > 0
&& max_ab > 1
&& max_bc > 1
&& max_ca > 1
&& max_abc >= 3
{
x += 1;
max_a -= 1;
max_b -= 1;
max_c -= 1;
max_ab -= 2;
max_bc -= 2;
max_ca -= 2;
max_abc -= 3;
}
max_a = max_a.min(k);
max_b = max_b.min(k);
max_c = max_c.min(k);
max_ab = max_ab.min(k);
max_bc = max_bc.min(k);
max_ca = max_ca.min(k);
max_abc = max_abc.min(k);
}
println!("{}", x);
}
