Canoes

You are organizing a canoe tour. Canoes can be hired at the harbour, and all of them are identical. A single canoe holds at most two people, and the combined weight of the people in it cannot exceed a fixed maximum. To keep the cost as low as possible, you must seat every participant using as few canoes as possible.

Write a program that:

• reads the maximum weight a canoe crew may have, the number of participants, and the weight of each participant from standard input,
• computes the minimum number of canoes needed to seat every participant under these rules,
• writes that result to standard output.

The first line contains one integer $w$, the maximum weight of a canoe crew ($80 \le w \le 200$). The second line contains one integer $n$, the number of participants ($1 \le n \le 30000$).

Each of the next $n$ lines contains one integer, the weight of a participant, which is between $5$ and $w$ inclusive.

Print a single integer on the first line: the minimum number of canoes that must be hired.