using System;
using System.Linq;
namespace y
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.ReadLine();
            var n = Console.ReadLine();
            var m = Console.ReadLine();
            var a = Math.Min(n.Count(x => x == 'A'), m.Count(x => x == 'A'));
            var b = Math.Min(n.Count(x => x == 'B'), m.Count(x => x == 'B'));
            Console.WriteLine(a + b);
        }
    }
}