n, m = map(int, input().split())
s = input()
t = input()
dp = list(range(m+1))
prev = 0
for i in range(1, n+1):
    prev = dp[0]
    dp[0] = i
    for j in range(1, m+1):
        dp[j] , prev = min(
                int(s[i-1]!=t[j-1]) + prev,
                1 + dp[j],
                1 + dp[j-1]), dp[j]
print(dp[m])