using System;
class MainClass
{
    public static void Main(string[] args)
    {

        string[] s1 = Console.ReadLine().Split(' ');
        int n = int.Parse(s1[0]);
        int m = int.Parse(s1[1]);
        string S = Console.ReadLine();
        string T = Console.ReadLine();

        int[,] dp = new int[n + 1, m + 1];

        for (int i = 0; i < n;i++)
        {
            for (int j = 0; j < m;j++)
            {
                if(S[i]==T[j])
                {
                    dp[i + 1, j + 1] = Math.Min(dp[i, j], dp[i + 1, j] + 1);
                    dp[i + 1, j + 1] = Math.Min(dp[i + 1, j + 1], dp[i, j + 1] + 1);
                }
                else
                {
                    dp[i + 1, j + 1] = Math.Min(dp[i, j] + 1, dp[i + 1, j] + 1);
                    dp[i + 1, j + 1] = Math.Min(dp[i + 1, j + 1], dp[i, j + 1] + 1);
                }

            }
        }

        Console.WriteLine(dp[n,m]);

    }
}