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