#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;

typedef int _loop_int;
#define REP(i,n) for(_loop_int i=0;i<(_loop_int)(n);++i)
#define FOR(i,a,b) for(_loop_int i=(_loop_int)(a);i<(_loop_int)(b);++i)
#define FORR(i,a,b) for(_loop_int i=(_loop_int)(b)-1;i>=(_loop_int)(a);--i)

#define DEBUG(x) cout<<#x<<": "<<x<<endl
#define DEBUG_VEC(v) cout<<#v<<":";REP(i,v.size())cout<<" "<<v[i];cout<<endl
#define ALL(a) (a).begin(),(a).end()

#define CHMIN(a,b) a=min((a),(b))
#define CHMAX(a,b) a=max((a),(b))

// mod
const ll MOD = 1000000007ll;
#define FIX(a) ((a)%MOD+MOD)%MOD

// floating
typedef double Real;
const Real EPS = 1e-11;
#define EQ0(x) (abs(x)<EPS)
#define EQ(a,b) (abs(a-b)<EPS)
typedef complex<Real> P;

int prime[25252];
int dp[25252];

int main(){
  int n;
  cin>>n;
  prime[0]=prime[1]=0;
  FOR(i,2,25252){
    bool flag = true;
    for(int x=2;x*x<=i;++x){
      if(i%x==0){
        flag = false;
        break;
      }
    }
    prime[i] = flag;
  }
  REP(i,25252)dp[i] = -1e9;
  dp[0] = 0;
  REP(j,25252){
    FORR(i,0,n){
      if(prime[j] && i+j<=n){
        CHMAX(dp[i+j],dp[i]+1);
      }
    }
  }
  if(dp[n]<0)dp[n]=-1;
  cout<<dp[n]<<endl;
  return 0;
}