import java.util.*;

class Main {
        public static void main(String args[]) {
                long[] dp = new long[20001];
                boolean[] prime = new boolean[20001];
                prime[0] = prime[1] = true;

                for (int i = 0; i < 20001; i++) {
                        dp[i] = (1 << 20) * -1;
                }

                dp[0] = 0;


                for (int i = 2; i < 20001; i++) {
                        if (!prime[i]) {
                                for (int j = 2; i * j < 20001; j++) {
                                        prime[i*j] = true;
                                }
                        }
                }

                for (int i = 20000; i >= 0; i--) {
                        if (!prime[i]) {
                                for (int j = 20000-i; j >= 0; j--) {
                                        dp[j+i] = Math.max(dp[j+i], dp[j] + 1);
                                }
                        }
                }

                try (Scanner sc = new Scanner(System.in)) {
                        long ans = dp[sc.nextInt()];
                        if (ans < 0) {
                                ans = -1;
                        }
                        System.out.println(ans);
                }
        }
}