require 'prime'

n = gets.strip.to_i

primes = []
primes << 2
i = 3
while i < n
	primes << i if i.prime?
	i += 2
end
# p primes.length

@memo = Hash.new(0)
@memo_next = Hash.new(0)
primes.each do |prime|
	@memo = @memo_next.clone
	@memo.each do |k, v|
		if k != n && k + prime > n
			@memo_next.delete(k)
			next	
		end
		next if k + prime != n && k + 2 * prime > n
		@memo_next[k + prime] = [@memo[k + prime], v + 1].max
		#print "#{prime} #{@memo_next}\n"
	end
	@memo_next[prime] = [1, @memo[prime]].max
	#@memo = @memo_next
end
if @memo_next.key?(n)
	p @memo_next[n]
else
	puts -1
end