N,M=map(int,input().split())
S=input()
T=input()

dp=[[10**18]*(M+1) for _ in range(N+1)]
dp[0][0]=0

for i in range(N+1):
    for j in range(M+1):
        if i>0:
            dp[i][j] = min(dp[i][j], dp[i-1][j]+1 )
        if j>0:
            dp[i][j] = min(dp[i][j], dp[i][j- 1]+1)
        if j>0 and i>0:
            dp[i][j] = min(dp[i][j], dp[i-1][j-1]+(S[i-1]!=T[j-1]))

print(dp[N][M])