蓝桥杯python：密码脱落

题目：
全部代码：

strs = input()
n = len(strs)
li = [[0] * n for i in range(n)]
for k in range(1, n + 1):
    for i in range(n):
        j=i+k-1
        if j>=n:
            break
        if k==1:
            li[i][j]=1
        else:
            li[i][j]=max(li[i][j-1], li[i][j])
            li[i][j]=max(li[i+1][j], li[i][j])
            if strs[i]==strs[j]:
                li[i][j]=max(li[i+1][j-1] + 2, li[i][j])
print(n-li[0][n-1])