require"prime"
n=gets.to_i
dp=Array.new(n+1)
dp[0]=0
max=temp=0
Prime.each(n){|p|
	0.upto(max){|k|
		next unless dp[k]
		temp=k+p
		break if temp>n+1
		dp[temp]=dp[k]+1 unless dp[temp]
	}
	max=temp
}
p dp[n]||-1