#include "bits/stdc++.h"
using namespace std;
#define FOR(i,j,k) for(int (i)=(j);(i)<(int)(k);++(i))
#define rep(i,j) FOR(i,0,j)
#define each(x,y) for(auto &(x):(y))
#define mp make_pair
#define mt make_tuple
#define all(x) (x).begin(),(x).end()
#define debug(x) cout<<#x<<": "<<(x)<<endl
#define smax(x,y) (x)=max((x),(y))
#define smin(x,y) (x)=min((x),(y))
#define MEM(x,y) memset((x),(y),sizeof (x))
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<ll> vll;

vector<int> sieve(int n){
    vector<bool> f(n+1);
    for(int i=3; i<=n; i+=2) f[i] = 1;
    for(int i=3; i<=sqrt(n); i+=2) if(f[i]) for(int j=i*3; j<=n; j+=i) f[j] = 0;
    vector<int> res;
    if(n >= 2)res.push_back(2);
    for(int i=3; i<=n; i+=2) if(f[i]) res.push_back(i);
    return res;
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);

    int n;
    while(cin >> n) {
        vi dp(n + 1, -1);
        vi ps = sieve(n);
        dp[0] = 0;
        each(p, ps) {
            for(int i = n - p; i >= 0; --i)if(dp[i] != -1) {
                smax(dp[i + p], dp[i] + 1);
            }
        }
        cout << dp[n] << endl;
    }
}