n, m = map(int, input().split())
S = input()
T = input()
dp = [[0]*(m+1) for _ in range(n+1)]

for i in range(n+1):
    dp[i][0] = i

for i in range(m+1):
    dp[0][i] = i

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

print(dp[n][m])