#include<bits//stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define req(i,n) for(int i = 1;i <=  n; i++)
#define rrep(i,n) for(ll i = n-1;i >= 0;i--)
#define ALL(obj) begin(obj), end(obj)
#define RALL(a) rbegin(a),rend(a)
typedef long long int ll;
typedef long double ld;
const int MAX = 510000;
const ll MOD = 1000000007;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
bool isPrime(int x){
    int i;
    if(x < 2)return 0;
    else if(x == 2) return 1;
    if(x%2 == 0) return 0;
    for(i = 3; i*i <= x; i += 2) if(x%i == 0) return 0;
    return 1;
}
int main(void) {
    int n,m;cin >>n;vector<int> dp(200000,-1);
    vector<int> p;
    req(i,20000) if(isPrime(i)) p.push_back(i);
    dp[0] = 0;
    for(int i:p){
        for(int j = n;j>=0;j--){
            if(i+j>n|| dp[j]==-1)continue;
            chmax(dp[i+j],dp[j]+1);
        }
    }cout << dp[n] <<endl;
}