#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<ll> VL;
typedef vector<VL> VVL;
typedef pair<int, int> PII;

#define FOR(i, a, n) for (int i = (int)a; i < (int)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define ALL(x) x.begin(), x.end()
#define MOD 1000000007
#define INF 1000000000
#define PI 3.14159265359
#define EPS 1e-12

int dp[20010];
vector<int> prime;
void p(int num) {
  for(int i=2; i<=num; ++i) {
    bool flag = true;
    for(int j=2; j<=sqrt(i); ++j) {
      if(i%j == 0) flag = false;
    }
    if(flag) prime.push_back(i);
  }
}

int main(void)
{
  int n;
  cin >> n;
  p(n);

  memset(dp, -1, sizeof(dp));
  dp[0] = 0;
  for(int i: prime) {
    for(int j=n; j>=0; --j) {
      if(j >= i && dp[j-i] != -1)
        dp[j] = max(dp[j], dp[j-i] + 1);
    }
  }
  cout << dp[n] << endl;
  return 0;
}