n, m = map(int, input().split())
s = str(input())
t = str(input())

INF = 10**18
dp = [[INF]*1010 for _ in range(1010)]
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])