using System.Numerics;

public class Program
{
    public static void Main()
    {

        //BigInteger num = BigInteger.Parse(Console.ReadLine() ?? string.Empty);
        //int num = int.Parse(Console.ReadLine() ?? string.Empty);
        string[] moji = (Console.ReadLine() ?? string.Empty).Trim().Split(' ');
        string str = Console.ReadLine() ?? string.Empty;
        string under = Console.ReadLine() ?? string.Empty;

        int up = int.Parse(moji[0]);
        int down = int.Parse(moji[1]);

        int count = 0;
        if(up <= down)
        {
            for(int i = 0;i < up;i++)
            {
                int index = under.IndexOf(str[i]);
                if(index >= 0)
                {
                    under = under.Remove(index, 1);
                    count++;
                }
            }
            Console.WriteLine(count);
        }
        else
        {
            for (int i = 0; i < down; i++)
            {
                int index = str.IndexOf(under[i]);
                if (index >= 0)
                {
                    str = str.Remove(index, 1);
                    count++;
                }
            }
            Console.WriteLine(count);

        }

    }
}