INF = 1000000
c = gets.to_i
n = gets.to_i
a = gets.split.map(&:to_i)
dp = Array.new(n + 1)
(n + 1).times{|i|
    dp[i] = Array.new(c + 1,INF)
    dp[i][0] = 0
    }

1.upto(n){|i|
    1.upto(a[i - 1] - 1){|j|
        dp[i][j] = dp[i - 1][j]
        }
    a[i - 1].upto(c){|j|
        dp[i][j] = [dp[i - 1][j], dp[i][j - a[i - 1]] + 1].min
        }
    }
if dp[n][c] == INF
    p -1
else
    p dp[n][c]
end