n,m=map(int,raw_input().split())
S=raw_input()
T=raw_input()
dp=[[10000 for i in range(m+1)] for j in range(n+1)]
dp[0][0]=0
for i in range(1,n+1):
    dp[i][0] = i
for j in range(1,m+1):
    dp[0][j]= j

for i in range(1, n+1):
    for j in range(1, m+1):
        if S[i-1]==T[j-1]:
            dp[i][j] = min(dp[i][j],dp[i-1][j-1])
        else:
            dp[i][j] = min(dp[i][j],1+dp[i-1][j-1])
        dp[i][j]=min(dp[i][j],dp[i-1][j]+1) # delete S[i]
        dp[i][j]=min(dp[i][j],dp[i][j-1]+1) # add T[j]
print dp[n][m]