#include <bits/stdc++.h>
using namespace std;
#define repd(i,a,b) for(int i=a;i<b;i++)
#define repds(i,a,b) for(int i=a+1;i<=b;i++)
#define rep(i,N) repd(i,0,N)
#define reps(i,N) repds(i,0,N)
#define debug(x) cout<<#x<<"="<<x<<endl
#define debugarr(arr,N,M){rep(i,N+1){rep(j,M+1){if(arr[i][j]==INF)printf(" INF");\
	else printf(" %3d",arr[i][j]);} cout<<endl;}}
#define pb push_back
#define pob pop_back
#define cint(a) int a;cin>>a
#define cint2(a,b) int a,b;cin>>a>>b
#define cint3(a,b,c) int a,b,c;cin>>a>>b>>c
#define chmax(a, b) a = (((a)<(b)) ? (b) : (a))
#define chmin(a, b) a = (((a)>(b)) ? (b) : (a))
typedef long long ll;
typedef pair<int,int> P;
const int INF=100000000;
const int dx[4]={ 0, 1, 0,-1};
const int dy[4]={ 1, 0,-1, 0};
//--------------------------------------//
int n;
vector<int> primes;
bool isPrime[2500];
int dp[20001];

int main(){
	cin>>n;
	memset(isPrime,1,n+1);
	isPrime[0]=isPrime[1]=false;
	repds(i,1,n){
		if(isPrime[i]){
			primes.pb(i);
			for(int j=i;j<n;j+=i) isPrime[j]=false;
		}
	}
	rep(i,n+1)
		rep(j,primes.size()+1){
			if(i==0)dp[i]=0;
			else dp[i]=-1;
		}
	for(auto p:primes)
		for(int i=n;i>0;i--){
			if(p + i <= n && dp[i] != -1){
                chmax(dp[p+i], dp[i] + 1);
            }
		}
	//debugarr(dp,n,primes.size());
	cout<<dp[n]<<endl;
	return 0;
}