require 'prime'

@n = gets.strip.to_i
@list = [2]
3.step(@n, 2) do |i|
	if i.prime?
		@list << i
	end
end
#p @list

@memo = Array.new(@n + 1, 0)
@list.each do |p|
	#p @memo
	@next_memo = @memo.clone
	(0..@n).each do |i|
		#p key, value
		if i + p > @n
			break
		end
		@next_memo[i + p] = [@memo[i + p], @memo[i] + 1].max 
	end
	@memo = @next_memo
end
#p @memo
if @memo[@n] != 0
	p @memo[@n]
else
	p -1
end