A9528 | 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.

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

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.