def solve(s1, s2):
    d = {}

    for i in range(len(s1)):
        d[i, 0] = i
    for j in range(len(s2)):
        d[0, j] = j

    for i in range(1, len(s1)):
        for j in range(1, len(s2)):
            n = 0 if s1[i] == s2[j] else 1
            d[i, j] = min(d[i - 1, j] + 1, d[i, j - 1] + 1, d[i - 1, j - 1] + n)

    return d[len(s1) - 1, len(s2) - 1]


def main():
    input()
    s1 = input()
    s2 = input()
    print(solve(s1, s2))


if __name__ == '__main__':
    main()