#include <bits/stdc++.h>
using namespace std;

#define _p(...) (void)printf(__VA_ARGS__)
#define forr(x,arr) for(auto&& x:arr)
#define _overload3(_1,_2,_3,name,...) name
#define _rep2(i,n) _rep3(i,0,n)
#define _rep3(i,a,b) for(int i=int(a);i<int(b);++i)
#define rep(...) _overload3(__VA_ARGS__,_rep3,_rep2,)(__VA_ARGS__)
#define _rrep2(i,n) _rrep3(i,0,n)
#define _rrep3(i,a,b) for(int i=int(b)-1;i>=int(a);i--)
#define rrep(...) _overload3(__VA_ARGS__,_rrep3,_rrep2,)(__VA_ARGS__)
#define all(x) (x).begin(), (x).end()
#define bit(n) (1LL<<(n))
#define sz(x) ((int)(x).size())
#define fst first
#define snd second
using ll=long long;using pii=pair<int,int>;
using vb=vector<bool>;using vs=vector<string>;
using vi=vector<int>;using vvi=vector<vi>;using vvvi=vector<vvi>;
using vl=vector<ll>;using vvl=vector<vl>;using vvvl=vector<vvl>;
using vd=vector<double>;using vvd=vector<vd>;using vvvd=vector<vvd>;
using vpii=vector<pii>;using vvpii=vector<vpii>;using vvvpii=vector<vvpii>;
template<typename T>T read(){T t;cin>>t;return t;}
template<class T,class U>ostream&operator<<(ostream&o,const pair<T,U>&p){o<<'('<<p.fst<<", "<<p.snd<<')';return o;}

// O(n log log n)
vector<int> sieve(int n) {
  vector<int> ret;
  if (n <= 2) return ret;
  vector<bool> ok(n / 2, true);
  ret.push_back(2);
  for (int i = 3; i < n; i += 2) {
    int i2 = i / 2;
    if (!ok[i2]) continue;
    ret.push_back(i);
    for (int j = i2 + i; j < n / 2; j += i) ok[j] = false;
  }
  return ret;
}

template<class T> bool amax(T &a, const T &b) { if (a < b) { a = b; return 1; } return 0; }

int solve() {
  int n = read<int>();
  auto ps = sieve(n+1);
  int m = sz(ps);

  vi dp(n+1, -1);
  dp[0] = 0;

  rep(i, m) {
    int p = ps[i];
    rrep(j, n) if (dp[j] >= 0) {
      if (j+p <= n) {
        amax(dp[j+p], dp[j] + 1);
      }
    }
  }

  return dp[n];
}

void Main() {
  cout << solve() << endl;
}
int main() { cin.tie(nullptr); ios::sync_with_stdio(false); Main(); return 0; }