package main

import (
	"bufio"
	"fmt"
	"os"
	"sort"
	"strconv"
)

func out(x ...interface{}) {
	fmt.Println(x...)
}

var sc = bufio.NewScanner(os.Stdin)

func getInt() int {
	sc.Scan()
	i, e := strconv.Atoi(sc.Text())
	if e != nil {
		panic(e)
	}
	return i
}

func getInts(N int) []int {
	ret := make([]int, N)
	for i := 0; i < N; i++ {
		ret[i] = getInt()
	}
	return ret
}

func getString() string {
	sc.Scan()
	return sc.Text()
}

// min, max, asub, absなど基本関数
func max(a, b int) int {
	if a > b {
		return a
	}
	return b
}

func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}

func asub(a, b int) int {
	if a > b {
		return a - b
	}
	return b - a
}

func abs(a int) int {
	if a >= 0 {
		return a
	}
	return -a
}

func lowerBound(a []int, x int) int {
	idx := sort.Search(len(a), func(i int) bool {
		return a[i] >= x
	})
	return idx
}

func upperBound(a []int, x int) int {
	idx := sort.Search(len(a), func(i int) bool {
		return a[i] > x
	})
	return idx
}

const inf = int(1e15)

var n, m int
var s, t string

func main() {
	sc.Split(bufio.ScanWords)
	sc.Buffer([]byte{}, 1000000)
	n, m = getInt(), getInt()
	s, t = getString(), getString()

	var dp [1010][1010]int
	for i := 0; i <= n; i++ {
		dp[i][0] = i
	}
	for i := 0; i <= m; i++ {
		dp[0][i] = i
	}

	for i := 0; i < n; i++ {
		for j := 0; j < m; j++ {
			if s[i] == t[j] {
				dp[i+1][j+1] = dp[i][j]
			} else {
				dp[i+1][j+1] = dp[i][j] + 1
			}
			dp[i+1][j+1] = min(dp[i+1][j+1], dp[i][j+1]+1)
			dp[i+1][j+1] = min(dp[i+1][j+1], dp[i+1][j]+1)
		}
	}
	out(dp[n][m])
}