INF = 10 ** 6
c,n = 2.times.map { gets.to_i}
a = gets.split.map(&:to_i)
dp = Array.new(c+1,INF)
dp[0] = 0
(1..c).each do |i|
    n.times do |j|
        if a[j] <= i && dp[i] > dp[i - a[j]] + 1
            dp[i] = dp[i - a[j]] + 1
        end
    end
end
puts dp[c] > c ? -1 : dp[c]