#include #include struct Prime { int max_n; std::vector primes; std::vector isp; explicit Prime(int max_n) : max_n(max_n), isp(max_n + 1, true) { isp[0] = isp[1] = false; for (int i = 2; i * i <= max_n; ++i) { if (isp[i]) { for (int j = i; i * j <= max_n; ++j) { isp[i * j] = false; } } } for (int p = 2; p <= max_n; ++p) { if (isp[p]) primes.push_back(p); } } template bool isprime(T n) const { if (n <= max_n) return isp[n]; for (T p : primes) { if (p * p > n) break; if (n % p == 0) return false; } return true; } template std::vector> factorize(T n) const { std::vector> facts; for (T p : primes) { if (p * p > n) break; if (n % p != 0) continue; int exp = 0; while (n % p == 0) { n /= p; ++exp; } facts.emplace_back(p, exp); } if (n > 1) { facts.emplace_back(n, 1); } return facts; } template std::vector divisors(T n) const { std::vector ret; for (T p = 1; p * p <= n; ++p) { if (n % p != 0) continue; ret.push_back(p); if (n / p == p) continue; ret.push_back(n / p); } return ret; } }; constexpr int INF = 1 << 30; void solve() { int n; std::cin >> n; auto ps = Prime(n).primes; std::vector dp(n + 1, -INF); dp[0] = 0; for (auto p : ps) { for (int x = n; x >= p; --x) { dp[x] = std::max(dp[x], dp[x - p] + 1); } } std::cout << std::max(dp[n], -1) << "\n"; } int main() { std::cin.tie(nullptr); std::ios::sync_with_stdio(false); solve(); return 0; }