n, m = map(int, input().split())
S = input()
T = input()

dp = [[i for i in range(m+1)]] + [[j]+[0]*m for j in range(1,n+1)]
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-1][j-1], dp[i][j-1]+1, dp[i-1][j]+1)
        else:
            dp[i][j] = min(dp[i-1][j-1]+1, dp[i][j-1]+1, dp[i-1][j]+1)

print(dp[-1][-1])