class Program
    {
        static void Main(string[] args)
        {
            int[] clothes = Array.ConvertAll(Console.ReadLine().Split(' '), num => int.Parse(num));
            string s = Console.ReadLine();
            int[] topCount = { 0, 0 };
            topCount = ClothesCount(s, topCount);
            string t = Console.ReadLine();
            int[] bottomCount = { 0, 0 };
            bottomCount = ClothesCount(t, bottomCount);
            int days = JudgeClothes(topCount,bottomCount);
            Console.WriteLine(days);
        }

        private static int JudgeClothes(int[] topCount, int[] bottomCount)
        {
            int days = 0;
            for( int i = 0; i < 2; i++)
            {
                if (topCount[i] < bottomCount[i])
                {
                    days += topCount[i];
                }
                else
                {
                    days += bottomCount[i];
                }
            }
            return days;
        }

        private static int[] ClothesCount(string clothers, int[] countList)
        {
            for(int i = 0; i < clothers.Length; i++)
            {
                if (clothers[i] == 'A')
                {
                    countList[0]++;
                }
                else
                {
                    countList[1]++;
                }
            }
            return countList;
        }
    }