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