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Language:
Ebbinghaus method
Time Limit: 1000MSMemory Limit: 10000K
Total Submissions: 371Accepted: 79

Description

Facer is going to have CET6 test! To prepare for the test, he bought a vocabulary book and divided it to 30 wordlist each contains about 60 words. However, this amount is too large for Facer because of his poor IQ. Recently, he found Ebbinghaus method, a famous way of memorizing. The method is like this: we label the day we first memorize the wordlist as first day, then we need to review the words in day 2, day 4, day 8,day 15 and day 30. After that, we will not forget them. Suppose memorizing a wordlist for the first time costs 1 hour and 20 minutes and reviewing costs 40 minutes. Now Facer wants a schedule of memorizing satisfying 2 conditions: 1) He can memorize all the words as soon as possible; 2) the memorizing time in each day should be no more than 2 hours. Now your task is to calculate how many days he needs to memorizing all words. Notice that Facer always memorize all the wordlist in sequence. For example, he will never memorize the third wordlist before the second one.

Input

The first line of the input contains n, m. n stands for the number of wordlist and m stand for the number of times Facer needs to review each wordlist.
Then next line contains an ascending integer sequence contains a1, a2, ..., am indicating on which day Facer needs to review the wordlist. The day is calculated from the day he first memorize it.
1 ≤ n, m ≤ 1000
ai+1 - ai ≤ 100
1 ≤ a1 ≤ 100

Output

Output the number of days Facer needs to memorizing all wordlists.

Sample Input

5 5
2 4 8 15 30

Sample Output

36

Source

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