#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define all(x) x.begin(),x.end()
#define rep(i,a,b) for(int i=a;i<=b;i++)
#define each(a,x) for (auto& x: a)
const char nl = '\n';
void solve(){
    int n; cin >> n;
    vector<bool> is_prime(n+1,true);
    is_prime[0] = is_prime[1] = false;
    vector<int> prime;
    rep(i,2,n) if (is_prime[i]) {
        prime.push_back(i);
        for (int j = i * i; j <= n; j+=i){
            is_prime[j] = false;
        }
    }
    vector<int> dp(n+1,-1);
    dp[0] = 0;
    each(prime,x){
        for (int i = n; i >= x; i--){
            if (dp[i - x] != -1) dp[i] = max(dp[i], dp[i - x] + 1);
        }
    }
    cout << dp[n];
}
int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    int t = 1; //cin >> t;
    while (t--){
        solve();
    }
}