require 'prime'
n = gets.chomp.to_i
#素数を固定して回す
max = 20001
dp = Array.new(max,0)
a = Prime.each(max).to_a.reverse.map(&:to_i)

a.each do |i|
    dp[i] += 1
end
a.each do |i|
    (max-1-i).downto(i+1) do |j|
        if dp[j] > 0
            dp[i+j] = [dp[j]+1,dp[i+j]].max
        end
    end
end
if dp[n] == 0
    puts "-1"
else
    puts dp[n]
end