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


class Template
{
	static Scanner sc;
	public static void Main(string[] args)
	{
		sc = new Scanner();
		var nm = sc.nextIntArray();
		int n = nm[0], m = nm[1];
		string S = sc.next();
		string T = sc.next();
		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] = (int)1e9;
			}
		}
		//dp[i, j] : Sのi文字目までと，Tのj文字目までのレーベンシュタイン距離
		for (int i = 0; i <= n; i++)
		{
			dp[i, 0] = i;
		}
		for (int i = 0; i <= m; i++)
		{
			dp[0, i] = i;
		}
		for (int i = 1; i <= n; i++)
		{
			for (int j = 1; j <= m; j++)
			{
				if (S[i - 1] != T[j - 1])
				{
					dp[i, j] = Math.Min(dp[i, j], dp[i - 1, j - 1] + 1);
				}
				else
				{
					dp[i, j] = Math.Min(dp[i, j], dp[i - 1, j - 1]);
				}
				dp[i, j] = Math.Min(dp[i, j], dp[i - 1, j] + 1);
				dp[i, j] = Math.Min(dp[i, j], dp[i, j - 1] + 1);
			}
		}
		Console.WriteLine(dp[n, m]);
	}
}

public class Scanner
{
	public Scanner() { }
	public string next()
	{
		return Console.ReadLine();
	}
	public int nextInt()
	{
		return int.Parse(next());
	}
	public double nextDouble()
	{
		return double.Parse(next());
	}
	public long nextLong()
	{
		return long.Parse(next());
	}
	public string[] nextArray()
	{
		return next().Split(' ');
	}
	public int[] nextIntArray()
	{
		return Array.ConvertAll(nextArray(), e => int.Parse(e));
	}
	public long[] nextLongArray()
	{
		return Array.ConvertAll(nextArray(), e => long.Parse(e));
	}
	public double[] nextDoubleArray()
	{
		return Array.ConvertAll(nextArray(), e => double.Parse(e));
	}
}