N,M = map(int,input().split())
S = input()
T = input()
INF = 10**9+7
dp = [[INF for j in range(M+1)]for i in range(N+1)]
for i in range(N+1):
	dp[i][0] = i
for i in range(M+1):
	dp[0][i] = i
for i in range(1,N+1):
	for j in range(1,M+1):
		dp[i][j] = min(dp[i][j],dp[i-1][j]+1)
		dp[i][j] = min(dp[i][j],dp[i][j-1]+1)
		dp[i][j] = min(dp[i][j],dp[i-1][j-1] + (0 if S[i-1] == T[j-1] else 1))
print(dp[N][M])