def main():
    n, m = map(int, input().split())
    s = input()
    t = input()

    # dp[i][j]:si番目までの文字列からtj番目までの文字列に変更する回数
    dp = [[0] * (m + 1) for _ in range(n + 1)]
    for j in range(1,m+1):
        dp[0][j] = j
    for i in range(1,n+1):
        dp[i][0] = i

    for i in range(n):
        si = s[i]
        for j in range(m):
            tj = t[j]
            if si == tj:
                dp[i + 1][j + 1] = min(dp[i][j], dp[i][j + 1] + 1, dp[i + 1][j] + 1)
            else:
                dp[i + 1][j + 1] = min(dp[i][j] + 1, dp[i][j + 1] + 1, dp[i + 1][j] + 1)
    print(dp[n][m])


main()