def read_data():
    n, m = map(int, input().split())
    S = input().strip()
    T = input().strip()
    return n, m, S, T

memo = dict()
def f(a, b, S, T):
    '''
    f(a, b, S, T) S[:a] を T[:b] に変更するのに必要な最低ステップ数
    '''
    global memo
    if (a, b) in memo:
        return memo[a, b]
    if a == 0:
        return b
    if b == 0:
        return a
    s = S[a - 1]
    t = T[b - 1]
    if s == t:
        memo[a, b] = f(a-1, b-1, S, T)
        return memo[a, b]
    if s != t:
        steps_change = 1 + f(a-1, b-1, S, T)
        steps_insert = 1 + f(a,   b-1, S, T)
        steps_delete = 1 + f(a-1, b,   S, T)
        memo[a, b] = min(steps_change, steps_insert, steps_delete)
        return memo[a, b]

if __name__ == '__main__':
    n, m, S, T = read_data()
    print(f(n, m, S, T))