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++) dp[i, j] = 1000;
        dp[0, 0] = 0;

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

                }
                if (i >= 0) dp[i + 1, j + 1] = Math.Min(dp[i + 1, j + 1], dp[i, j + 1] + 1);
                if (j >= 0) dp[i + 1, j + 1] = Math.Min(dp[i + 1, j + 1], dp[i + 1, j] + 1);

            }
        }

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

    }
}