UVA13004 At most twice

Description

[problemUrl]: https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=866&page=show_problem&problem=4892 [PDF](https://uva.onlinejudge.org/external/130/p13004.pdf) ![](https://cdn.luogu.com.cn/upload/vjudge_pic/UVA13004/d0308aa05abc31a671c5c654cf3fa7959d4e0032.png)

Input Format

![](https://cdn.luogu.com.cn/upload/vjudge_pic/UVA13004/e706b2524947dbbab79305600a1927f9bf850e7c.png)

Output Format

![](https://cdn.luogu.com.cn/upload/vjudge_pic/UVA13004/a46a8aede09e45615469ff1579f88b38cf619971.png)