#include<bits/stdc++.h>
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>
using namespace std;
using namespace __gnu_pbds;
struct custom_hash {
    static uint64_t splitmix64(uint64_t x) {
        x += 0x9e3779b97f4a7c15;
        x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
        x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
        return x ^ (x >> 31);
    }

    size_t operator()(uint64_t x) const {
        static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();
        return splitmix64(x + FIXED_RANDOM);
    }
};
typedef tree<int, null_type, greater<int>, rb_tree_tag, tree_order_statistics_node_update> pbds; // find_by_order, order_of_key
//find by order-> element at ith idx(starting from 0)//gives iterator to that index//if not present *it gives 0
//order of key-> number of element less than a number
#define int long long int 
// #define ll long long int
#define loop(s, e) for(int i = s; i < e; i++)
#define rloop(e, s) for(int i = e; i>= s; i--)
#define v vector<int>
// #define vll vector<long long int>
#define printyes cout<<"YES\n"
#define printno cout<<"NO\n"
//COMMENT THIS FOR INTERACTIVE PROBLEMS...............
#define endl '\n'
#define mod 1000000007
#define pinf 1e18
#define ninf -1e18
#define printvec(arr) cout<<#arr<<"=> [ ";for(int i = 0; i < arr.size(); i++){cout<<arr[i]<<" ";}cout<<"]"<<endl;
#define dbg(x) cout<<"value of "<<#x<<" is => "<<x<<endl;
#define all(x) x.begin(), x.end()
#define vpii vector<pair<int, int>>
#define pii pair<int,int>
#define pll pair<ll, ll>
#define ff first
#define ss second
#define pb push_back
#define vpll vector<pll>
#define here(i) cout<<"here "<<i<<" "<<endl;
#define rt return;
#define mx max_element
#define mn min_element
#define asum accumulate
int delrow[4] = {-1,0,1,0};
int delcol[4] = {0,1,0,-1};

void printv(v& ans) {
    for(auto it: ans)cout<<it<<" ";
    cout<<endl;
}

int setBit(int n, int bitNo) {
  n = (n|(1LL<<bitNo));
  return n;
}

int currBit(int n, int bitNo) {
  return ((n&(1ll<<bitNo)) == 0)?0:1;
}

int unSetBit(int n, int bitNo) {
  n = (n&(~(1ll<<bitNo)));
  return n;
}
//*************************************************CHECK THE CONSTRAINTS**********************************************************//
int f(int a, int b) {
  if(b == 0)return 1;
  int res = f(a, b/2);
  if(b%2 != 0) {
    return (((res)%mod * (res)%mod)%mod * a)%mod;
  }
  else {
    return ((res)%mod * (res)%mod)%mod;
  }
}

vector<bool> sieve(int n) {
  vector<bool> prime(n+1, 1);
  prime[0] = 0;
  prime[1] = 0;
  for(int i = 2; i*i <= n; i++) {
    if(prime[i] == 1) {
      for(int j = i*i; j <= n; j+=i) {
        prime[j] = 0;
      }
    }
  }
  return prime;
}

void pikachu(int tt, int tc) {
  int n;
  cin>>n;
  vector<bool> p = sieve(n);
  vector<int> primes;
  for(int i = 0; i <= n; i++) {
    if(p[i])primes.pb(i);
  }
  vector<vector<int>> dp(2, vector<int>(n+1, -1));
  dp[0][0] = 0;
  dp[0][2] = 1;
  for(int i = 1; i < primes.size(); i++) {
    for(int num = 0; num <= n; num++) {
      if(num - primes[i] >= 0 && dp[0][num - primes[i]] != -1) 
      dp[1][num] = max(dp[1][num], dp[0][num-primes[i]] + 1);
      dp[1][num] = max(dp[1][num], dp[0][num]);
    }
    dp[0] = dp[1];
    for(auto &e: dp[1])e = -1;
    dp[1][0] = 0;
  }
  cout<<(dp[0][n])<<endl;
}


int32_t main() {
  ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
  #ifndef ONLINE_JUDGE
      freopen("input.txt", "r", stdin);
      freopen("output.txt", "w", stdout);
  #endif
  int gsBall = 1;
  // cin>>gsBall;
  int tt = gsBall;
  int tc = 1;
  while(gsBall--) {
    pikachu(tt, tc);
    tc++;
  }
  return 0;
}