import java.util.*; import java.io.*; public class Main { public static void main(String[] args) { FastScanner sc = new FastScanner(); int n = sc.nextInt(); List prime = new ArrayList<>(); for (int i = 2; i <= n; i++) { boolean isPrime = true; for (int j = 2; j * j <= i; j++) { if (i % j == 0) { isPrime = false; } } if (isPrime) { prime.add(i); } } long[] dp = new long[n + 1]; Arrays.fill(dp, -1); dp[0] = 0; for (int i : prime) { for (int j = n; j >= 0; j--) { if (dp[j] < 0 || i + j > n) { continue; } dp[i + j] = Math.max(dp[i + j], dp[j] + 1); } } // System.out.println(Arrays.toString(dp)); System.out.println(dp[n]); } } class FastScanner { private final InputStream in = System.in; private final byte[] buffer = new byte[1024]; private int ptr = 0; private int buflen = 0; private boolean hasNextByte() { if (ptr < buflen) { return true; } else { ptr = 0; try { buflen = in.read(buffer); } catch (IOException e) { e.printStackTrace(); } if (buflen <= 0) { return false; } } return true; } private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1; } private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126; } public boolean hasNext() { while (hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++; return hasNextByte(); } public String next() { if (!hasNext()) throw new NoSuchElementException(); StringBuilder sb = new StringBuilder(); int b = readByte(); while (isPrintableChar(b)) { sb.appendCodePoint(b); b = readByte(); } return sb.toString(); } public long nextLong() { if (!hasNext()) throw new NoSuchElementException(); long n = 0; boolean minus = false; int b = readByte(); if (b == '-') { minus = true; b = readByte(); } if (b < '0' || '9' < b) { throw new NumberFormatException(); } while (true) { if ('0' <= b && b <= '9') { n *= 10; n += b - '0'; } else if (b == -1 || !isPrintableChar(b)) { return minus ? -n : n; } else { throw new NumberFormatException(); } b = readByte(); } } public int nextInt() { long nl = nextLong(); if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) throw new NumberFormatException(); return (int) nl; } public double nextDouble() { return Double.parseDouble(next()); } }