using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace YukiCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            var nn = Console.ReadLine().Split().Select(int.Parse).ToArray();
            var sa = Console.ReadLine();
            var sb = Console.ReadLine();
            int na = Math.Min(sa.Count(c => c == 'A'), sb.Count(c => c == 'A'));
            int nb = Math.Min(sa.Count(c => c == 'B'), sb.Count(c => c == 'B'));
            Console.WriteLine(na + nb);
            Console.ReadLine();
        }
    }
}