n, m = map(int, input().split())
S = input()
T = input()

dp = [[float('inf') for _ in range(m + 1)] for _ in range(n + 1)]
dp[0][0] = 0
for i in range(-1, n):
    for j in range(-1, m):
        if i == -1 and j == -1:
            continue
        if i >= 0 and j >= 0:
            if S[i] == T[j]:
                dp[i + 1][j + 1] = min(dp[i + 1][j + 1], dp[i][j])
            else:
                dp[i + 1][j + 1] = min(dp[i + 1][j + 1], dp[i][j] + 1)
        if i >= 0:
            dp[i + 1][j + 1] = min(dp[i + 1][j + 1], dp[i][j + 1] + 1)
        if j >= 0:
            dp[i + 1][j + 1] = min(dp[i + 1][j + 1], dp[i + 1][j] + 1)
print(dp[n][m])