using System;

public class hello
{
    public static void Main()
    {
        string[] line = Console.ReadLine().Trim().Split(' ');
        var n = int.Parse(line[0]);
        var m = int.Parse(line[1]);
        var s = Console.ReadLine().Trim();
        var na = getA(s);
        var nb = n - na;
        var t = Console.ReadLine().Trim();
        var ma = getA(t);
        var mb = m - ma;
        Console.WriteLine(Math.Min(na, ma) + Math.Min(nb, mb));
    }
    public static int getA(string s) => s.Length - s.Replace("A", "").Length;
}