n,m = map(int,input().split())
s = input()
t = input()


dp = [[float("inf") for i in range(m+1)] for j in range(n+1)]
dp[0][0] = 0
dp[1][0] = 1
dp[0][1] = 1
for i in range(n):
    for j in range(m):
        if s[i]==t[j]:
            dp[i+1][j+1] = min(dp[i][j], dp[i][j+1]+1, dp[i+1][j]+1)
        else:
            dp[i+1][j+1] = min(dp[i][j]+1, dp[i][j+1]+1, dp[i+1][j]+1)
print(dp[n][m])