C = gets.to_i
N = gets.to_i
a = gets.split.map(&:to_i)
dp = Array.new(C + 1, Float::INFINITY)
dp[0] = 0
a.each do |x|
  (0..C-x).each do |y|
    dp[y + x] = [dp[y + x], dp[y] + 1].min
  end
end
ans = if dp [C] < Float::INFINITY
        dp[C]
      else
        -1
      end
puts ans