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

#define ll long long
#define vvi vector<vector<int>>
#define vec vector
#define pq priority_queue
#define all(v) (v).begin(), (v).end()
#define rep(i, n) for (int (i) = (0); (i) < (n); ++(i))
#define repp(i, m, n) for (int (i) = (m); (i) < (n); ++(i))
#define debug(x) cerr << #x << ": " << x << endl;
#define debug2(x, y) cerr<<"("<<#x<<", "<<#y<<") = "<<"("<<x<<", "<<y<<")"<<endl;
#define debug3(x, y, z) cerr<<"("<<#x<<", "<<#y<<", "<<#z<<") = "<<"("<<x<<", "<<y<<", "<<z<<")"<<endl;
#define debugB(x, y) cerr<<#x<<": "<<bitset<y>(x) << endl;
#define line() cerr << "---------------" << endl;

const int dx[] = {1, -1, 0, 0};
const int dy[] = {0, 0, -1, 1};

template<typename T>
void printA(vector<T> &printArray, char between = ' ') {
   int paSize = printArray.size();
   for (int i = 0; i < paSize; i++) { cerr << printArray[i] << between;}
   if (between != '\n') {cerr << endl;}
}

// ------------------------------------------------------------------------------------------

void init(vec<int> &prime) {
   prime.push_back(2);
   for (int i = 3; i <= 20000; i++) {
      bool ok = true;
      for (int j = 2; j < i; j++) {
         if (i % j == 0) {
            ok = false;
            break;
         }
      }
      if (ok) prime.push_back(i);
   }
}

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

   vec<int> primes;
   init(primes);
   vec<int> dp(n+1, -1);
   dp[0] = 0;
	for(int p : primes) {
		for(int i = n - p; i >= 0; -- i) {
         if(dp[i] != -1) {
            dp[i + p] = max(dp[i + p], dp[i] + 1);
         }
      }
	}
	cout << dp[n] << endl;

   return 0;
}