# include <bits/stdc++.h>
# define FILE(x) freopen(x ".in", "r", stdin); freopen(x ".out", "w", stdout);
using namespace std;
const int N = 2e4 + 10;
int n;
int f[N];
vector < int > prime;
bool p[N];
void init()
{
    for (int i = 2; i <= n; i ++)
    {
        if (!p[i])
        {
            prime.push_back(i);
        }
        for (int j = 0; j < prime.size() && prime[j] * i <= n; j ++)
        {
            p[i * prime[j]] = 1;
            if (i % prime[j] == 0) break;
        }
    }
}
void solve()
{
    cin >> n;
    init();
    fill(f + 1, f + 1 + n, -1e9);
    for (int x : prime)
    {
        for (int i = n; i >= 0; i --) 
        {
            if (x + i <= n) f[i + x] = max(f[i + x], f[i] + 1);
        }
    }
    cout << (f[n] < 0 ? -1 : f[n]);
}   
int main()
{
    ios :: sync_with_stdio(0);
    cin.tie(0), cout.tie(0);
    int T = 1;
    while (T --) solve();
    return 0;
}