#include<iostream>
#include<algorithm>
#include<vector>


using namespace std;

int main(){
	int N;
	cin >> N;
	vector<bool> isPrime(N+1,true);
	isPrime[0] = false;
	isPrime[1] = false;

	for(int i=2; i*i <= N; i++){
		if(isPrime[i])
			for(int j = i+i; j <= N; j+=i){
				isPrime[j] = false;
			}
	}
	vector<int> primes;
	for(int i = 2; i <= N;i++)
		if(isPrime[i])
			primes.push_back(i);

	vector<int> dp(N+1, -1);
	dp[0] = 0;
	for(int p:primes){
		for(int j = N; j>=0; j--){
			if(p + j <= N && dp[j] !=-1){
				dp[p + j] = (dp[p+j] > dp[j] + 1) ? dp[p+j] : dp[j] + 1;
			}
		}
	}

	cout << dp[N] << endl;
	return 0;
}