use std::io::{stdin, Read};
use std::cmp::min;

fn main() {
    let mut buf = String::new();
    stdin().read_to_string(&mut buf).unwrap();
    let mut tok = buf.split_whitespace();
    let mut get = || tok.next().unwrap();
    macro_rules! get {
        ($t:ty) => (get().parse::<$t>().unwrap());
        () => (get!(usize));
    }

    let n = get!();
    let m = get!();
    let s = get().as_bytes();
    let t = get().as_bytes();
    let sa = s.iter().filter(|ch| **ch == b'A').count();
    let ta = t.iter().filter(|ch| **ch == b'A').count();
    let sb = n - sa;
    let tb = m - ta;
    let ans = min(sa, ta) + min(sb, tb);
    println!("{}", ans);
}