import numpy as np

N, M = map(int, input().split())
S = np.array(list(input()))
T = np.array(list(input()))

min1 = np.frompyfunc(lambda x, y: min(x, y) + 1, 2, 1)

eq = (S[:, None] == T[None, :])
dp = np.zeros((N + 1, M + 1), dtype=int)
dp[0] = np.arange(M + 1)
dp[:, 0] = np.arange(N + 1)
for i in range(N):
    dp[i + 1, 1:] = np.minimum(dp[i, 1:], dp[i, :-1] - eq[i])
    dp[i + 1] = min1.accumulate(dp[i + 1], dtype=np.int64)
print(dp[N, M])