#yuki_225

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]