def resolve():
    import sys
    input = sys.stdin.readline
    n, m = map(int, input().split())
    a = [ord(x) - ord("a") for x in input()]
    b = [ord(x) - ord("a") for x in input()]
    INF = float('inf')
    dp = [[INF] * (m + 1) for _ in range(n + 1)]
    for i in range(n):
        dp[i][0] = i
    for i in range(1, m):
        dp[0][i] = i
    for i in range(n):
        for j in range(m):
            if a[i] == b[j]:
                dp[i + 1][j + 1] = dp[i][j]
            else:
                dp[i + 1][j + 1] = min(dp[i][j],
                                       dp[i][j + 1],
                                       dp[i + 1][j]) + 1
    print(dp[-1][-1])


if __name__ == '__main__':
    resolve()