CF439A.Devu, the Singer and Churu, the Joker

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题目描述

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.

输入格式

The first line contains two space separated integers $n$ , $d$ $(1<=n<=100; 1<=d<=10000)$ . The second line contains $n$ space-separated integers: $t_{1},t_{2},...,t_{n}$ $(1<=t_{i}<=100)$ .

输出格式

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.

输入输出样例

输入#1
```
3 30
2 2 1
```
输出#1
```
5
```
输入#2
```
3 20
2 1 1
```
输出#2
```
-1
```

说明/提示

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.

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