n, m = map(int,raw_input().split(" "))
S = raw_input()
T = raw_input()
dp = [[0 for i in xrange(n+1)] for j in range(m+1)]
for i in xrange(n+1):
	dp[0][i] = i
for i in xrange(1,m+1):
	dp[i][0] = i
for i in xrange(1,m+1):
	for j in xrange(1,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]