Pasha has a wooden stick of some positive integer length n. He wants to perform exactly three cuts to get four parts of the stick. Each part must have some positive integer length and the sum of these lengths will obviously be n. 

Pasha likes rectangles but hates squares, so he wonders, how many ways are there to split a stick into four parts so that it's possible to form a rectangle using these parts, but is impossible to form a square.

Your task is to help Pasha and count the number of such ways. Two ways to cut the stick are considered distinct if there exists some integer x, such that the number of parts of length x in the first way differ from the number of parts of length x in the second way.

Input

The first line of the input contains a positive integer n (1 ≤ n ≤ 2·109) — the length of Pasha's stick.

Output

The output should contain a single integer — the number of ways to split Pasha's stick into four parts of positive integer length so that it's possible to make a rectangle by connecting the ends of these parts, but is impossible to form a square. 

Examples

Input

6


Output

1


Input

20


Output

4

Note

There is only one way to divide the stick in the first sample {1, 1, 2, 2}.

Four ways to divide the stick in the second sample are {1, 1, 9, 9}, {2, 2, 8, 8}, {3, 3, 7, 7} and {4, 4, 6, 6}. Note that {5, 5, 5, 5} doesn't work.
import java.util.*;
import java.io.*;
import java.math.*;
import java.util.regex.Matcher;
//linkedhashmap contains the entry in the same order which we are giving and not in sorted way like in hashmaps
public class CF {
    FastScanner in;
    PrintWriter out;
    final static int M=1000001;
    public ArrayList<Integer> input(int m){
        ArrayList<Integer> li= new ArrayList<>();
        for(int i=0;i<m;i++)
            li.add(in.nextInt());
        return li;
    }
    class Pair{
        int x;
        int y;
    }
    public class pair<T,V> {
        private T x;
        private V y;

        public void setY(V y) {
            this.y = y;
        }

        public V getY() {
            return y;
        }

        public void setX(T x) {
            this.x = x;
        }

        public T getX() {
            return x;
        }
    }
    Set<Long> primeFactors(long n)
    {
        // Print the number of 2s that divide n
        Set<Long> li=new HashSet<>();

        while (n%2 == 0)
        {
            li.add(2L);
            n = n/2;
        }

        // n must be odd at this point.  So we can skip one element (Note i = i +2)
        for (long i = 3; i <= Math.sqrt(n); i = i+2)
        {
            // While i divides n, print i and divide n
            while (n%i == 0)
            {
                li.add(i);
                n = n/i;
            }
        }

        // This condition is to handle the case whien n is a prime number
        // greater than 2
        if (n > 2)
            li.add(n);
        return li;
    }
    int res[];
    void sieve(){
        res=new int[10000009];

        int p[]=new int[10000009];
        for(int i=2;i<=10000000;i++){
            if(p[i]==0){
                for(int j=i+i;j<=10000000;j+=i){
                    if(p[i]==0){
                        p[j]=i;
                    }
                    res[i]=res[i-1]+i;
                }
            }
            else{
                res[i]=res[i-1]+p[i];
            }
        }
    }
    public static HashSet<String> getAllPermutations(String str) {

        HashSet<String> permutations = new HashSet<String>();

        if(str == null || str.length() == 0) {
            permutations.add("" );
            return permutations;
        }

        char first = str.charAt(0);
        String remainingString = str.substring(1);
        HashSet<String> words = getAllPermutations(remainingString);
        for(String word: words) {
            for(int i = 0; i <= word.length(); i++) {
                String prefix = word.substring(0, i);
                String suffix = word.substring(i);
                permutations.add(prefix + first + suffix);
            }
        }
        return permutations;
    }

    //    static class Pair<T> {
//        T a;
//        T b;
//
//        public Pair(T a, T b) {
//            this.a = a;
//            this.b = b;
//        }
//    }
    private ArrayList<Integer> adj[];
    private boolean visited[];
    // private boolean visited1[];
    private LinkedList<Integer> q;
    private int level[];
    private int f=0;
    void initialize(){
        visited=new boolean[20001];
        //visited1=new boolean[10001];
        level =new int[20001];
        Arrays.fill(visited,false);
    }
    void solve() {
        int n=in.nextInt();
        if(n%2==1){
            System.out.println(0);
        }
        else{
            if(n%4==0){
                System.out.println(n/4 - 1);
            }
            else
                System.out.println(n/4);
        }
    }
    private int[] calculateZ(char input[]) {
        int Z[] = new int[input.length];
        int left = 0;
        int right = 0;

        for(int k = 1; k < input.length; k++) {
            if(k > right) {
                left = right = k;
                while(right < input.length && input[right] == input[right - left]) {
                    right++;
                }
                Z[k] = right - left;
                right--;
            } else {
//we are operating inside box
                int k1 = k - left;
//if value does not stretches till right bound then just copy it.
                if(Z[k1] <= right - k + 1) {
                    Z[k] = Z[k1];
                } else { //otherwise try to see if there are more matches.
                    left = k;
                    while(right < input.length && input[right] == input[right - left]) {
                        right++;
                    }
                    Z[k] = right - left;
                    right--;
                }
            }
        }
        return Z;
    }

    void bfs1(int i){
        q=new LinkedList<>();
        q.add(i);
        visited[i]=true;
        while(!q.isEmpty()){
            int s=q.peekFirst();
            q.removeFirst();
            for(int j=0;j<adj[s].size();j++){
                if(!visited[adj[s].get(j)]){
                    level[adj[s].get(j)]=(level[s]+1);
                    q.add(adj[s].get(j));
                    visited[adj[s].get(j)]=true;
                }

            }
        }
    }
    int bfs(int i){
        q=new LinkedList<>();
        q.add(i);
        visited[i]=true;int g=0;
        while(!q.isEmpty()){
            int s=q.peekFirst();
            if(q.size()==1 && adj[s].size()==1)
            {
                g=s;
            }
            q.removeFirst();
            for(int j=0;j<adj[s].size();j++){
                if(!visited[adj[s].get(j)]){
                    //level[adj[s].get(j)]=level[s]+1;
                    q.add(adj[s].get(j));
                    visited[adj[s].get(j)]=true;
                }
            }
        }
        return g;
    }
    boolean dfs(int i,int parent){
        visited[i]=true;
        for(int j=0;j<adj[i].size();j++){
            if(adj[i].get(j)==parent && visited[i])
                continue;
            if(!visited[adj[i].get(j)]) {
                f++;
            }
            if(dfs(adj[i].get(j),i)){
                return true;
            }
        }
        return false;
    }
    static boolean isPali(StringBuilder s){
        for(int i = 0; i < (s.length() >> 1); i++)
            if(s.charAt(i) != s.charAt(s.length() - 1 - i))
                return false;
        return true;
    }
    void run(){
        try {
            in = new FastScanner(new File("B.in"));
            out = new PrintWriter(new File("B.out"));
            solve();
            out.close();
        }
        catch(FileNotFoundException e){
            e.printStackTrace();
        }
    }

    void runIO(){
        in = new FastScanner(System.in);
        out = new PrintWriter(System.out);

        solve();
        out.close();
    }
    class FastScanner{
        BufferedReader br;
        StringTokenizer st;
        public FastScanner(File f){
            try{
                br = new BufferedReader(new FileReader(f));
            }
            catch(FileNotFoundException e){
                e.printStackTrace();
            }
        }
        public FastScanner(InputStream f){
            br = new BufferedReader(new InputStreamReader(f));
        }
        String next(){
            while(st==null || !st.hasMoreTokens()){
                String s = null;
                try{
                    s= br.readLine();
                }
                catch(IOException e){
                    e.printStackTrace();
                }
                if(s==null)
                    return null;
                st = new StringTokenizer(s);
            }
            return st.nextToken();
        }

        boolean hasMoreTokens(){
            while(st==null || !st.hasMoreTokens()){
                String s = null;
                try{
                    s= br.readLine();
                }
                catch(IOException e){
                    e.printStackTrace();
                }
                if(s==null)
                    return false;
                st = new StringTokenizer(s);
            }
            return true;
        }
        int nextInt(){
            return Integer.parseInt(next());
        }
        long nextLong(){
            return Long.parseLong(next());
        }
        double nextDouble(){
            return Double.parseDouble(next());
        }
    }

    public static void main(String[] args) {
        new CF().runIO();
    }
}