n, m = map(int,raw_input().split(" "))
S = list(raw_input())
T = list(raw_input())
dp = [[1000 for i in range(n+1)] for j in range(m+1)]
for i in range(n+1):
	dp[0][i] = i
for i in range(1,m+1):
	dp[i][0] = i
for i in range(1,m+1):
	for j in range(n+1):
		dp[i][j] = min(dp[i][j-1]+1, dp[i-1][j]+1, dp[i-1][j-1]+(T[i-1]!=S[j-1]))
print dp[m][n]