n, m = [int(i) for i in input().split()]
s, t = input(), input()

# dp[i+1][j+1]: sのi文字目までを変換してtのj文字目までを作る最小操作回数
dp = [[float("inf")]*(m+1) for _ in range(n+1)]
dp[0][0] = 0
for i in range(1, n+1):
    dp[i][0] = i
for j in range(1, m+1):
    dp[0][j] = j

for i in range(n):
    for j in range(m):
        if s[i] == t[j]:
            dp[i+1][j+1] = min(
                dp[i+1][j+1],
                dp[i][j+1] + 1,
                dp[i+1][j] + 1,
                dp[i][j]
            )
        else:
            dp[i+1][j+1] = min(
                dp[i+1][j+1],
                dp[i][j+1] + 1,
                dp[i+1][j] + 1,
                dp[i][j] + 1
            )
print(dp[-1][-1])