#include <bits/stdc++.h>
using namespace std;
#define int long long
#define INF -1145141919810
#define REP(i,n) for (int i=0;i<(n);i++)
typedef pair<int,int> P;

int N;
int dp[20100]={};
vector<int> prime;
int generate(){
  prime.push_back(2);
  for(int i=3;i<=N;i+=2){
    int k=0;
    for(int j=3;j<=sqrt(i);j+=2){
      if(i%j==0){
        k=1;
        break;
      }
    }
    if(k==0) prime.push_back(i);
  }
  return 0;
}

signed main(){
  cin>>N;
  generate();
  for(int i=0;i<prime.size();i++){
    for(int j=20099;j>=0;j--){
      if(dp[j]!=0&&prime[i]+j<=N){
         dp[prime[i]+j]=max(dp[prime[i]+j],dp[j]+1);
       }
    }
    dp[prime[i]]=max(dp[prime[i]],(int)1);
  }
  if(dp[N]==0) dp[N]=-1;
  cout<<dp[N]<<endl;
}