#include "bits/stdc++.h"
using namespace std;
#define print(x) cout<<x<<endl;
#define rep(i,a,b) for(int i=a;i<b;i++)
#define REP(i,a) for(int i=0;i<a;i++)
typedef long long ll;
typedef pair<int, int> PI;
typedef pair<int, PI> V;
typedef vector<int> VE;
const ll mod = 1000000007;

vector<int> prime;
bool is_prime[20002];

int sieve(int n){
  int p=0;
  REP(i,n+1)is_prime[i]=true;
  is_prime[0]=is_prime[1]=false;
  rep(i,2,n+1){
      if(is_prime[i]){
      //print(i);
      prime.push_back(i);
      for(int j=2*i;j<=n;j+=i) is_prime[j]=false;
    }
  }
  return p;
}

int main(){
  int n;
  cin>>n;
  int dp[20002];
  bool flag[20002];
  memset(dp,-1,sizeof(dp));
  int p=sieve(n);
  dp[0]=0;

  for(auto u : prime){
    for(int j=n;j>=0;j--){
      if(u+j<=n&&dp[j]!=-1){
        dp[u+j]=max(dp[u+j],dp[j]+1);
      }
    }
  }
  print(dp[n]);
}