CF439A.Devu, the Singer and Churu, the Joker

Devu is a renowned classical singer. He is invited to many big functions/festivals. Recently he was invited to "All World Classical Singing Festival". Other than Devu, comedian Churu was also invited.

Devu has provided organizers a list of the songs and required time for singing them. He will sing n songs, i__th song will take t__i minutes exactly.

The Comedian, Churu will crack jokes. All his jokes are of 5 minutes exactly.

People have mainly come to listen Devu. But you know that he needs rest of 10 minutes after each song. On the other hand, Churu being a very active person, doesn't need any rest.

You as one of the organizers should make an optimal sсhedule for the event. For some reasons you must follow the conditions:

• The duration of the event must be no more than d minutes;
• Devu must complete all his songs;
• With satisfying the two previous conditions the number of jokes cracked by Churu should be as many as possible.

If it is not possible to find a way to conduct all the songs of the Devu, output -1. Otherwise find out maximum number of jokes that Churu can crack in the grand event.

德武是一位著名的古典歌手，他受邀参加许多大型活动或节日。最近，他被邀请参加“全球古典歌唱节”。除了德武之外，喜剧演员楚鲁也被邀请出席。

德武已向主办方提供了一份歌曲列表以及演唱每首歌所需的时间。他将演唱 $n$ 首歌，其中第 $i$ 首歌恰好耗时 $t_i$ 分钟。

喜剧演员楚鲁则负责讲笑话，他每个笑话的时长恰好为 5 分钟。

观众主要是来听德武演唱的。但众所周知，德武每唱完一首歌后都需要休息 10 分钟。而楚鲁则非常活跃，不需要任何休息时间。

作为主办方之一，你需要为本次活动制定一个最优的日程安排。出于某些原因，你必须满足以下条件：

• 活动总时长不得超过 $d$ 分钟；
• 德武必须完整演唱全部歌曲；
• 在满足上述两个条件的前提下，楚鲁所讲的笑话数量应尽可能多。

如果无法安排使得德武能完整演唱所有歌曲，则输出 -1；否则，请计算出楚鲁在本次盛会中最多能讲多少个笑话。

The first line contains two space separated integers n, d (1 ≤ n ≤ 100; 1 ≤ d ≤ 10000). The second line contains n space-separated integers: _t_1, _t_2, ..., t__n (1 ≤ t__i ≤ 100).

第一行包含两个用空格分隔的整数 $n$、$d$（$1 ≤ n ≤ 100$；$1 ≤ d ≤ 10000$）。第二行包含 $n$ 个用空格分隔的整数：$t_1,\,t_2,\,...,\,t_n$（$1 ≤ t_i ≤ 100$）。

If there is no way to conduct all the songs of Devu, output -1. Otherwise output the maximum number of jokes that Churu can crack in the grand event.

如果无法演唱 Devu 的所有歌曲，则输出 -1；否则输出 Churu 在盛大活动中能讲的最大笑话数量。

Consider the first example. The duration of the event is 30 minutes. There could be maximum 5 jokes in the following way:

• First Churu cracks a joke in 5 minutes.
• Then Devu performs the first song for 2 minutes.
• Then Churu cracks 2 jokes in 10 minutes.
• Now Devu performs second song for 2 minutes.
• Then Churu cracks 2 jokes in 10 minutes.
• Now finally Devu will perform his last song in 1 minutes.

Total time spent is 5 + 2 + 10 + 2 + 10 + 1 = 30 minutes.

Consider the second example. There is no way of organizing Devu's all songs. Hence the answer is -1.

考虑第一个例子。活动持续时间为 30 分钟。最多可以讲 5 个笑话，具体安排如下：

• 首先，Churu 用 5 分钟讲一个笑话。
• 接着，Devu 演唱第一首歌曲，耗时 2 分钟。
• 然后，Churu 用 10 分钟讲 2 个笑话。
• 接下来，Devu 演唱第二首歌曲，耗时 2 分钟。
• 然后，Churu 再用 10 分钟讲 2 个笑话。
• 最后，Devu 演唱最后一首歌曲，耗时 1 分钟。

总耗时为 $5 + 2 + 10 + 2 + 10 + 1 = 30$ 分钟。

考虑第二个例子。不存在一种方式能安排 Devu 的所有歌曲。因此答案为 $-1$。