n, m = map(int, input().split())
s = input()
t = input()
dp = [[0]*(m+2) for _ in range(n+1)]
for i in range(n+1)[::-1]:
    for j in range(m+1)[::-1]:
        res = 1001
        if i == n and j == m:
            dp[i][j] = 0
            continue
        if i < n and j < m:
            res = min(res, int(s[i]!=t[j]) + dp[i+1][j+1])
        if i < n:
            res = min(res, 1 + dp[i+1][j])
        if j < m:
            res = min(res, 1 + dp[i][j+1])
        dp[i][j] = res
print(dp[0][0])