import sys
sys.setrecursionlimit(10**6)
slen, tlen = map(int, input().split())
s = input()
t = input()

dp = [[None] * tlen for _ in range(slen)]
def dfs(a=slen - 1, b=tlen - 1):
    if a == b == -1:
        return 0
    if a == -1:
        return b + 1
    if b == -1:
        return a + 1

    if dp[a][b] is not None:
        return dp[a][b]
    r = min(
        dfs(a - 1, b) + 1,
        dfs(a, b - 1) + 1,
        dfs(a - 1, b - 1) + (s[a] != t[b]),
    )
    dp[a][b] = r
    return r

print(dfs())