import java.io.*; import java.util.*; public class Main { public static void main(String[] args) throws Exception { Scanner sc = new Scanner(); int n = sc.nextInt(); boolean[] isNotPrimes = new boolean[n + 1]; int[] counts = new int[n + 1]; int max = 0; Arrays.fill(counts, -1); counts[0] = 0; for (int i = 2; i <= n; i++) { if (!isNotPrimes[i]) { for (int j = Math.min(max, n - i); j >= 0; j--) { if (counts[j] >= 0) { counts[j + i] = Math.max(counts[j + i], counts[j] + 1); max = Math.max(max, j + i); } } for (int j = 2; j * i <= n; j++) { isNotPrimes[j * i] = true; } } } System.out.println(counts[n]); } } class Scanner { BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); StringTokenizer st = new StringTokenizer(""); StringBuilder sb = new StringBuilder(); public Scanner() throws Exception { } public int nextInt() throws Exception { return Integer.parseInt(next()); } public long nextLong() throws Exception { return Long.parseLong(next()); } public double nextDouble() throws Exception { return Double.parseDouble(next()); } public String next() throws Exception { while (!st.hasMoreTokens()) { st = new StringTokenizer(br.readLine()); } return st.nextToken(); } }