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.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.*;

/**
 * Created by dhamada on 15/06/10.
 */
public class C {
    public static void main(String[] args) {
        InputReader in = new InputReader(System.in);
        PrintWriter out = new PrintWriter(System.out);

        int n = in.nextInt();
        int[] pair = new int[n+1];
        Arrays.fill(pair, -1);
        pair[1] = Integer.MAX_VALUE;

        int[] pr = generatePrimes(200000);
        List<int[]> ans = solveA(n, pr);

        out.println(ans.size());
        for (int[] l : ans) {
            out.println(l[0] + " " + l[1]);
        }
        out.flush();
    }

    static List<int[]> solveA(int n, int[] pr) {
        int[] pair = new int[n+1];
        Arrays.fill(pair, -1);
        pair[1] = 1;

        List<int[]> ans = new ArrayList<>();
        for (int p = pr.length-1 ; p >= 0 ; p--) {
            int d = pr[p];
            List<Integer> lf = new ArrayList<>();
            int now = d;
            while (now <= n) {
                if (pair[now] == -1) {
                    lf.add(now);
                }
                now += d;
            }
            Collections.sort(lf, new Comparator<Integer>() {
                @Override
                public int compare(Integer o1, Integer o2) {
                    return (o2 % 2) - (o1 % 2);
                }
            });
            for (int i = 0 ; i+1 < lf.size() ; i += 2) {
                int a = lf.get(i);
                int b = lf.get(i+1);
                pair[a] = b;
                pair[b] = a;
                ans.add(new int[]{a, b});
            }
        }
        return ans;
    }

    static int[] generatePrimes(int upto) {
        boolean[] isp = new boolean[upto];
        Arrays.fill(isp, true);

        int pi = 0;
        for (int i = 2; i < upto ; i++) {
            if (isp[i]) {
                pi++;
                for (int j = i * 2; j < upto; j += i) {
                    isp[j] = false;
                }
            }
        }

        int[] ret = new int[pi];
        int ri = 0;
        for (int i = 2 ; i < upto ; i++) {
            if (isp[i]) {
                ret[ri++] = i;
            }
        }
        return ret;
    }

    static class InputReader {
        private InputStream stream;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;

        public InputReader(InputStream stream) {
            this.stream = stream;
        }

        private int next() {
            if (numChars == -1)
                throw new InputMismatchException();
            if (curChar >= numChars) {
                curChar = 0;
                try {
                    numChars = stream.read(buf);
                } catch (IOException e) {
                    throw new InputMismatchException();
                }
                if (numChars <= 0)
                    return -1;
            }
            return buf[curChar++];
        }

        public char nextChar() {
            int c = next();
            while (isSpaceChar(c))
                c = next();
            if ('a' <= c && c <= 'z') {
                return (char)c;
            }
            if ('A' <= c && c <= 'Z') {
                return (char)c;
            }
            throw new InputMismatchException();
        }

        public String nextToken() {
            int c = next();
            while (isSpaceChar(c))
                c = next();
            StringBuilder res = new StringBuilder();
            do {
                res.append((char)c);
                c = next();
            } while (!isSpaceChar(c));
            return res.toString();
        }

        public int nextInt() {
            int c = next();
            while (isSpaceChar(c))
                c = next();
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = next();
            }
            int res = 0;
            do {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = next();
            } while (!isSpaceChar(c));
            return res * sgn;
        }

        public long nextLong() {
            int c = next();
            while (isSpaceChar(c))
                c = next();
            long sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = next();
            }
            long res = 0;
            do {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = next();
            } while (!isSpaceChar(c));
            return res * sgn;
        }

        public boolean isSpaceChar(int c) {
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }

        public interface SpaceCharFilter {
            public boolean isSpaceChar(int ch);
        }
    }

    static void debug(Object... o) {
        System.err.println(Arrays.deepToString(o));
    }
}