N,M=map(int,input().split())
A=input()
B=input()

INF=2**60
dp=[[INF]*(M+1) for i in range(N+1)]
#print(dp)

for i in range(N+1):
    dp[i][0]=i
for j in range(M+1):
    dp[0][j]=j
for i in range(N):
    for j in range(M):
        #置換
        dp[i+1][j+1]=min(dp[i+1][j+1],dp[i][j]+(0 if A[i]==B[j] else 1))
        #削除A
        dp[i+1][j+1]=min(dp[i+1][j+1],dp[i][j+1]+1)
        #削除B
        dp[i+1][j+1]=min(dp[i+1][j+1],dp[i+1][j]+1)
        
        #print(dp)


print(dp[N][M])