c = gets.to_i
n = gets.to_i
a = gets.split.map &:to_i

INF = 10**9
dp = Array.new(c + 1, INF)
dp[0] = 0

a.each do |x|
	(c + 1 - x).times { |i| dp[i + x] = dp[i] + 1 if dp[i + x] > dp[i] + 1 }
end

puts dp[c] != INF ? dp[c] : -1