func main()
	var n: int :: cui@inputInt()
	var isPrime: []bool :: @sieve(n)
	var dp: []int :: #[n + 1]int
	for p(2, n)
		if(isPrime[p])
			for i(n, 2, -1)
				if(dp[i] <> 0)
					if(i + p <= n)
						do dp[i + p] :: lib@max(dp[i + p], dp[i] + 1)
					end if
				end if
			end for
			do dp[p] :: lib@max(dp[p], 1)
		end if
	end for
	var m: int :: dp[n] = 0 ?(-1, dp[n])
	do cui@print("\{m}\n")
end func

func sieve(n: int): []bool
	if(n < 2)
		ret [false].repeat(n + 1)
	end if
	var res: []bool :: [false, false] ~ [true].repeat(n - 1)
	for i(2, n)
		if(res[i])
			var j: int :: i * i
			while(j <= n)
				do res[j] :: false
				do j :+ i
			end while
		end if
	end for
	ret res
end func