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.io.*;
import java.util.*;
import java.math.*;

public class Main implements Runnable {
    public InputReader in;
    public PrintWriter out;


    public void solve() throws Exception {
        // solution goes here
        int N = in.nextInt();
        int x = N / 4;
        if (x * 4 == N)
            x--;
        out.print(N % 2 == 0 ? x : 0);
    }

    public void run() {
        try {
            in = new InputReader(System.in);
            out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));
            Locale.setDefault(Locale.US);
            solve();
            out.close();
        } catch (Throwable e) {
            e.printStackTrace();
            System.exit(7);
        }
    }

    static int abs(int x) {
        return x < 0 ? -x : x;
    }

    static int max(int a, int b) {
        return a > b ? a : b;
    }

    static int min(int a, int b) {
        return a < b ? a : b;
    }

    public static void main(String args[]) {
        new Thread(null, new Main(), "Main", 1 << 28).start();
    }

    static boolean OJ = System.getProperty("ONLINE_JUDGE") != null;

    public void console(Object... objects) {
        if (!OJ) {
            out.println(Arrays.deepToString(objects));
            out.flush();
        }
    }

    @SuppressWarnings({"Duplicates", "unused"})
    static class InputReader {

        private InputStream stream;
        private byte[] buf = new byte[2048];
        private int curChar;
        private int numChars;
        private SpaceCharFilter filter;

        public InputReader() {
            this.stream = System.in;
        }

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

        public InputReader(SpaceCharFilter filter) {
            this.stream = System.in;
            this.filter = filter;
        }

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

        public int read() {
            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 = read();
            while (isSpaceChar(c))
                c = read();
            return (char) c;
        }

        public int nextDigit() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            return c - '0';
        }

        public int nextInt() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            boolean negative = false;
            if (c == '-') {
                negative = true;
                c = read();
            }
            int res = 0;
            do {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));
            return negative ? -res : res;
        }

        public int[] nextInts(int N) {
            int[] nums = new int[N];
            for (int i = 0; i < N; i++)
                nums[i] = nextInt();
            return nums;
        }

        public long[] nextLongs(int N) {
            long[] nums = new long[N];
            for (int i = 0; i < N; i++)
                nums[i] = nextLong();
            return nums;
        }

        public int nextUnsignedInt() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            int res = 0;
            do {
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));
            return res;
        }

        public final long nextLong() {
            int c = read();
            while (isSpaceChar(c)) {
                c = read();
            }
            boolean negative = false;
            if (c == '-') {
                negative = true;
                c = read();
            }
            long res = 0;
            do {
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));
            return negative ? -res : res;
        }

        public final long nextUnsignedLong() {
            int c = read();
            while (isSpaceChar(c)) {
                c = read();
            }
            long res = 0;
            do {
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));
            return res;
        }

        public double nextDouble() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            long sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            long res = 0;
            do {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            } while (!(c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1 || c == '.'));

            if (c != '.') {
                return res * sgn;
            }
            c = read();

            long aft = 0;
            int len = 1;
            do {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                aft *= 10;
                len *= 10;
                aft += c - '0';
                c = read();
            } while (!isSpaceChar(c));

            return res * sgn + aft / (1.0 * len);
        }

        public String nextLine() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            StringBuilder res = new StringBuilder();
            do {
                res.appendCodePoint(c);
                c = read();
            } while (!isEndChar(c));
            return res.toString();
        }

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

        public boolean isEndChar(int c) {
            if (filter != null)
                return filter.isSpaceChar(c);
            return c == '\n' || c == '\r' || c == '\t' || c == -1;
        }

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

        public char[] nextChars() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            StringBuilder res = new StringBuilder();
            do {
                res.appendCodePoint(c);
                c = read();
            } while (!isSpaceChar(c));

            char[] chars = new char[res.length()];
            res.getChars(0, chars.length, chars, 0);
            return chars;
        }

        public int[][] nextIntMatrix(int rows, int cols) {
            int[][] matrix = new int[rows][cols];
            for (int i = 0; i < rows; i++)
                for (int j = 0; j < cols; j++)
                    matrix[i][j] = nextInt();
            return matrix;
        }

        public long[][] nextLongMatrix(int rows, int cols) {
            long[][] matrix = new long[rows][cols];
            for (int i = 0; i < rows; i++)
                for (int j = 0; j < cols; j++)
                    matrix[i][j] = nextLong();
            return matrix;
        }

        public char[][] nextCharMap(int rows, int cols) {
            char[][] matrix = new char[rows][cols];
            for (int i = 0; i < rows; i++)
                for (int j = 0; j < cols; j++)
                    matrix[i][j] = nextChar();
            return matrix;
        }

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