_ = input()
S = input()
T = input()
INF = 10**7

dp = [[INF]*(len(T)+1) for _ in range(len(S)+1)]
dp[0][0] = 0

for i in range(len(S)+1):
    for j in range(len(T)+1):
        if i > 0 and j > 0:
            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], dp[i-1][j-1]+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)
print(dp[len(S)][len(T)])