input：

1 1 2 1 1 3

answer：

2

死亡题解：

• https://www.luogu.com.cn/blog/xiaolou/p1349-ti-xie TLE
• https://www.luogu.com.cn/blog/cjyyb/solution-p1349 MLE
• https://www.luogu.com.cn/blog/user3091/solution-p1349 TLE
• https://www.luogu.com.cn/blog/HOJQVFNA/solution-p1349 WA
• https://www.luogu.com.cn/blog/xiaohuang/solution-p1349 TLE