Problem: Jzzhu has picked n apples from his big apple tree. All the apples are numbered from 1 to n. Now he wants to sell them to an apple store. 

Jzzhu will pack his apples into groups and then sell them. Each group must contain two apples, and the greatest common divisor of numbers of the apples in each group must be greater than 1. Of course, each apple can be part of at most one group.

Jzzhu wonders how to get the maximum possible number of groups. Can you help him?

Input

A single integer n (1 ≤ n ≤ 105), the number of the apples.

Output

The first line must contain a single integer m, representing the maximum number of groups he can get. Each of the next m lines must contain two integers — the numbers of apples in the current group.

If there are several optimal answers you can print any of them.

Examples

Input

6


Output

2
6 3
2 4


Input

9


Output

3
9 3
2 4
6 8


Input

2


Output

0

Solution (in JAVA):

Solution:
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.PriorityQueue;
import java.util.Random;
import java.util.Scanner;
import java.util.Stack;
import java.util.StringTokenizer;
import java.util.TreeMap;
import java.util.TreeSet;
import java.lang.Long;
import java.math.BigDecimal;
import java.math.BigInteger;

/**
 * Problem statement: http://codeforces.com/problemset/problem/431/D
 * 
 * @author thepham
 * 
 */

public class C_Round_257_Div1 {
	static long Mod = 1000000007;

	public static void main(String[] args) throws FileNotFoundException {
		// PrintWriter out = new PrintWriter(new FileOutputStream(new File(
		// "output.txt")));
		PrintWriter out = new PrintWriter(System.out);
		Scanner in = new Scanner();
		int n = in.nextInt();
		boolean[] check = new boolean[n + 1];
		ArrayList<Integer>[] p = new ArrayList[n + 1];
		PriorityQueue<Node>[] q = new PriorityQueue[n + 1];
		int result = 0;
		StringBuilder builder = new StringBuilder();
		for (int i = 2; i <= n; i++) {
			if (p[i] == null) {
				p[i] = new ArrayList();
				q[i] = new PriorityQueue();
				for (long j = i; j <= n; j += i) {
					if (p[(int) j] == null) {
						p[(int) j] = new ArrayList();
					}
					p[(int) j].add(i);

				}
			}
		}
		PriorityQueue<Node> list = new PriorityQueue();
		for (int i = 2; i <= n; i++) {
			list.add(new Node(i, p[i].size()));
			if (q[i] != null) {
				for (long j = i + i; j <= n; j += i) {
					q[i].add(new Node((int) j, p[(int) j].size()));
				}
			}
		}

		while(!list.isEmpty()) {
			Node node = list.poll();
			int i = node.val;
			if (!check[i]) {
				int min = -1;
				check[i] = true;
				for (int j : p[i]) {
					while (!q[j].isEmpty() && check[q[j].peek().val]) {
						q[j].poll();
					}
					if (!q[j].isEmpty()) {
						if (min == -1
								|| p[min].size() > q[j].peek().num
								|| (p[min].size() == q[j].peek().num && min > q[j]
										.peek().val)) {
							min = q[j].peek().val;
						}
					}
				}
				if (min != -1) {
					check[min] = true;
					result++;
					// System.out.println(p[min].size());
					builder.append(i).append(" ").append(min).append("\n");
				}
			}
		}
		out.println(result);
		out.println(builder.toString());
		out.close();
	}

	static class Node implements Comparable<Node> {

		int val, num;

		public Node(int val, int num) {
			this.val = val;
			this.num = num;
		}

		@Override
		public int compareTo(Node o) {
			if (num != o.num) {
				return num - o.num;
			}
			return val - o.val;
		}
	}

	static class Segment implements Comparable<Segment> {
		int x, y;

		public Segment(int x, int y) {
			super();
			this.x = x;
			this.y = y;
		}

		public String toString() {
			return x + " " + y;
		}

		@Override
		public int compareTo(Segment o) {
			if (x != o.x) {
				return x - o.x;
			}
			return o.y - y;
		}
	}

	public static int[] buildKMP(String val) {
		int[] data = new int[val.length() + 1];
		int i = 0;
		int j = -1;
		data[0] = -1;
		while (i < val.length()) {
			while (j >= 0 && val.charAt(i) != val.charAt(j)) {
				j = data[j];
			}
			i++;
			j++;

			data[i] = j;
			// System.out.println(val + " " + i + " " + data[i]);
		}
		return data;
	}

	static int find(int index, int[] u) {
		if (u[index] != index) {
			return u[index] = find(u[index], u);
		}
		return index;
	}

	static int crossProduct(Point a, Point b) {
		return a.x * b.y + a.y * b.x;
	}

	static long squareDist(Point a) {
		long x = a.x;
		long y = a.y;
		return x * x + y * y;
	}

	static Point minus(Point a, Point b) {
		return new Point(a.x - b.x, a.y - b.y);
	}

	public static boolean nextPer(int[] data) {
		int i = data.length - 1;
		while (i > 0 && data[i] < data[i - 1]) {
			i--;
		}
		if (i == 0) {
			return false;
		}
		int j = data.length - 1;
		while (data[j] < data[i - 1]) {
			j--;
		}
		int temp = data[i - 1];
		data[i - 1] = data[j];
		data[j] = temp;
		Arrays.sort(data, i, data.length);
		return true;
	}

	static class Point {
		int x, y;

		public Point(int x, int y) {
			super();
			this.x = x;
			this.y = y;
		}

		public String toString() {
			return "{" + x + " " + y + "}";
		}

	}

	static long gcd(long a, long b) {
		if (b == 0) {
			return a;
		}
		return gcd(b, a % b);
	}

	public static class FT {

		int[] data;

		FT(int n) {
			data = new int[n];
		}

		public void update(int index, int value) {
			while (index < data.length) {
				data[index] += value;
				index += (index & (-index));
			}
		}

		public int get(int index) {
			int result = 0;
			while (index > 0) {
				result += data[index];
				index -= (index & (-index));
			}
			return result;

		}
	}

	static class Scanner {

		BufferedReader br;
		StringTokenizer st;

		public Scanner() throws FileNotFoundException {
			// System.setOut(new PrintStream(new
			// BufferedOutputStream(System.out), true));
			br = new BufferedReader(new InputStreamReader(System.in));
			// br = new BufferedReader(new InputStreamReader(new
			// FileInputStream(
			// new File("input.txt"))));
		}

		public String next() {

			while (st == null || !st.hasMoreTokens()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (Exception e) {
					throw new RuntimeException();
				}
			}
			return st.nextToken();
		}

		public long nextLong() {
			return Long.parseLong(next());
		}

		public int nextInt() {
			return Integer.parseInt(next());
		}

		public double nextDouble() {
			return Double.parseDouble(next());
		}

		public String nextLine() {
			st = null;
			try {
				return br.readLine();
			} catch (Exception e) {
				throw new RuntimeException();
			}
		}

		public boolean endLine() {
			try {
				String next = br.readLine();
				while (next != null && next.trim().isEmpty()) {
					next = br.readLine();
				}
				if (next == null) {
					return true;
				}
				st = new StringTokenizer(next);
				return st.hasMoreTokens();
			} catch (Exception e) {
				throw new RuntimeException();
			}
		}
	}

}