import std.algorithm.comparison;
import std.conv;
import std.stdio;
import std.string;


const int MAX_N = 20000;
const int UNDEF = -1;
immutable PRIMES = sieveOfEratosthenes(MAX_N);


pure @safe int[] sieveOfEratosthenes(const int end){
	assert(end > 1);
	auto isPrime = new bool[](end);
	isPrime[] = true;
	isPrime[0] = false;
	isPrime[1] = false;
	int[] primes;
	for (int i = 2; i < end; i++){
		if (isPrime[i]){
			primes ~= i;
			for (int j = 2 * i; j < end; j += i){
				isPrime[j] = false;
			}
		}
	}
	return primes;
}


pure @safe int compute(const int n){
	auto dp = new int[](n + 1);
	dp[] = UNDEF;
	dp[0] = 0;
	foreach (prime; PRIMES){
		if (prime > n) {
			break;
		}
		for (int i = n - 1; i >= 0; i--) {
			if (dp[i] != UNDEF && i + prime < n + 1){
				dp[i + prime] = max(dp[i + prime], dp[i] + 1);
			}
		}
	}
	return dp[n];
}


void main(){
	readln.chomp.to!int.compute.writeln;
}