using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Text;
using System.Text.RegularExpressions;
using System.Linq;
using System.IO;

class Program
{
    static void Main(string[] args)
    {
        new Magatro().Solve();
    }
}

class Magatro
{
    public void Solve()
    {
        Console.ReadLine();
        string s = Console.ReadLine();
        string t = Console.ReadLine();
        Console.WriteLine(LenenshteinDistance(s, t));
    }


    private int LenenshteinDistance(string a, string b)
    {
        int[,] dp = new int[a.Length + 1, b.Length + 1];

        for (int i = 0; i <= a.Length; i++)
        {
            dp[i, 0] = i;
        }

        for (int i = 0; i <= b.Length; i++)
        {
            dp[0, i] = i;
        }

        for (int i = 1; i <= a.Length; i++)
        {
            for (int j = 1; j <= b.Length; j++)
            {
                int cost = a[i - 1] == b[j - 1] ? 0 : 1;

                dp[i, j] = (new int[] { dp[i - 1, j] + 1, dp[i, j - 1]+1, dp[i - 1, j - 1] + cost }).Min();
            }
        }

        return dp[a.Length, b.Length];
    }
}