#include using namespace std; using ll = long long; using VI = vector; using VL = vector; using VS = vector; using VVI = vector; using VVL = vector; using PII = std::pair; using PLL = std::pair; #define rep(i, n) for (int i = 0; i < (int)(n); i++) #define repr(i, n) for (int i = (int)(n)-1; i >= 0; i--) #define rep2(i, s, n) for (int i = (s); i < (int)(n); i++) #define rep3(i, s, n, d) for (int i = (s); i < (int)(n); i += (d)) #define allpt(v) (v).begin(), (v).end() #define allpt_c(v) (v).cbegin(), (v).cend() #define allpt_r(v) (v).rbegin(), (v).rend() const int mod = 1e9 + 7, mod2 = 998244353, mod3 = 1e9 + 9; const ll inf = 1e18; const string wsp = " "; const string tb = "\t"; const string rt = "\n"; template void show1dvec(const vector &v) { if (v.size() == 0) return; int n = v.size() - 1; rep(i, n) cout << v[i] << wsp; cout << v[n] << rt; return; } template void show2dvec(const vector> &v) { int n = v.size(); rep(i, n) show1dvec(v[i]); } template void show1dpair(const vector> &v) { int n = v.size(); rep(i, n) cout << v[i].first << wsp << v[i].second << rt; return; } template void pairzip(const vector> &v, vector &t, vector &s) { int n = v.size(); rep(i, n) { t.push_back(v[i].first); s.push_back(v[i].second); } return; } template void maxvec(vector &v) { T s = v[0]; int n = v.size(); rep(i, n - 1) { if (s > v[i + 1]) { v[i + 1] = s; } s = v[i + 1]; } } template bool myfind(T t, S s) { return find(t.cbegin(), t.cend(), s) != t.cend(); } bool check(int y, int x, int h, int w) { return 0 <= y && y < h && 0 <= x && x < w; } template vector cumsum(const vector &v) { T s = 0; vector ret = {0}; rep(i, v.size()) { s += v[i]; ret.push_back(s); } return ret; } bool iskadomatsu(int a, int b, int c) { return (a != b && b != c && c != a) && ((a > b && b < c) || (a < b && b > c)); } VS split(string s, char c) { VS ret; string part; s += c; rep(i, s.length()) { if (s[i] == c) { ret.emplace_back(part); part = ""; } else if (s[i] != c) { part += s[i]; } } return ret; } string removezero(string &s) { string ret; for (auto z : s) if (z != '0') ret += z; return ret; } ll sumdigit(ll x) { ll ans{0}; while (x > 0) { ans += x % 10; x /= 10; } return ans; } template ll pow_mod(T p, S q, R mod) { ll ret = 1, r = p; while (q) { if (q % 2) ret *= r, ret %= mod; r = (r * r) % mod, q /= 2; } return ret % mod; } ll comb(int a, int b, const VL &frac_list, const VL &frac_inv_list) { ll ret = frac_list[a]; ret *= frac_inv_list[b]; ret %= mod; ret *= frac_inv_list[a - b]; ret %= mod; return ret; } void shave(vector &v, int n) { vector x, y; int n_sq = sqrt(n) + 1; for (int i = 3; i < n + 1; i += 2) { x.emplace_back(i); } for (int i = 3; i < n_sq; i += 2) { for (auto itr = x.begin(); itr != x.end(); itr++) { if (*itr == i || *itr % i != 0) y.emplace_back(*itr); } x.clear(); x = y; y.clear(); } if (n >= 2) x.insert(x.begin(), 2); for (auto itr = x.begin(); itr != x.end(); itr++) { v.emplace_back(*itr); } } int main() { cin.tie(0); ios::sync_with_stdio(false); #ifdef DEBUG cout << "DEBUG MODE" << endl; ifstream in("input.txt"); //for debug cin.rdbuf(in.rdbuf()); //for debug #endif ll n, m, p; cin >> n; VI prime_list; shave(prime_list, n); m = prime_list.size(); VVI dp(m + 1, VI(n + 1, -1e6)); dp[0][n] = 0; rep(i, m) repr(j, n + 1) { p = prime_list[i]; if (j - p >= 0) dp[i + 1][j - p] = max(dp[i + 1][j - p], dp[i][j] + 1); dp[i + 1][j] = max(dp[i + 1][j], dp[i][j]); } // show2dvec(dp); // show1dvec(prime_list); cout << (dp[m][0] == -1e6 ? -1 : dp[m][0]) << rt; return 0; }