#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define loop(i,a,b) for(i=a;i<b;i++)
#define rloop(i,a,b) for(i=a;i>=b;i--)
#define vi vector<int>
#define vl vector<ll>
#define vii vector< vector<int> >
#define vll vector< vector<ll> >
#define vs vector<string>
const int inf=1000000001;
const ll INF=1e16;
#define MOD 1000000007
#define mod 1000000009
#define pi 3.14159265358979323846

int main(){
  int n,i,j;
  cin>>n;
  vi sosuu;
  vi moto(n+1);
  loop(i,0,n+1){
    moto[i]=i;
  }
  moto[0]=moto[1]=-1;
  loop(i,2,n+1){
    if(moto[i]!=-1){
      bool flag=false;
      loop(j,2,sqrt(i+1)){
	if(i%j==0){
	  flag=true;
	  break;
	}
      }
      if(flag==false){
	sosuu.push_back(i);
	loop(j,1,n/i+1){
	  moto[i*j]=-1;
	}
      }
    }
  }
  vector<int> dp(n+1,-1);
  dp[0]=0;
  loop(i,0,sosuu.size()){
    rloop(j,n-sosuu[i],0){
      if(dp[j]!=-1){
	dp[j+sosuu[i]]=max(dp[j+sosuu[i]],dp[j]+1);
      }
    }
  }
  cout<<dp[n]<<endl;
}