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.text.*;
import java.math.*;
import java.util.regex.*;
import java.lang.*;

public class P610A {
    //static long mod=1000000007;
    
    public static void main(String[] args) throws Exception{            
         InputReader in = new InputReader(System.in);       
        PrintWriter pw=new PrintWriter(System.out);   
        
        //int t=in.readInt();
        //  while(t-->0)
            //{
            int n=in.readInt();
        long ans=0;
        if(n%2==1||n<=3)
            pw.println(ans);        
        else
        {
            ans=n/4;
            if(n%4==0)
                ans--;
            pw.println(ans);    
        }
        
           //pw.println(" ");           
        
        //}
                    
        
        pw.close();
    }
    
         
    public static long  ways(int n, int r, long MOD)
    {
      //  vector<long long> f(n + 1,1);
        long f[]=new long[n+1];
        Arrays.fill(f,1);
        for (int i=2; i<=n;i++)
            f[i]= (f[i-1]*i) % MOD;
        return (f[n]*((InverseEuler(f[r], MOD) * InverseEuler(f[n-r], MOD)) % MOD)) % MOD;
    }
    public static long  InverseEuler(long n, long MOD)
    {
        return pow(n,MOD-2,MOD);
    }
    static boolean isPrime(int number) {
        if (number <= 1) {
            return false;
        }
        if (number <= 3) {
            return true;
        }
        if (number % 2 == 0 || number % 3 == 0) {
            return false;
        }
        int i = 5;
        while (i * i <= number) {
            if (number % i == 0 || number % (i + 2) == 0) {
                return false;
            }
            i += 6;
        }
        return true;
    }
    
public static long gcd(long x,long y)
{
    if(x%y==0)
        return y;
    else
        return gcd(y,x%y);
}
    
public static int gcd(int x,int y)
{
    if(x%y==0)
        return y;
    else 
        return gcd(y,x%y);
}
public static int abs(int a,int b)
{
    return (int)Math.abs(a-b);
}
public static long abs(long a,long b)
{
    return (long)Math.abs(a-b);
}
public static int max(int a,int b)
{
    if(a>b)
        return a;
    else
        return b;
}
public static int min(int a,int b)
{
    if(a>b)
        return b;
    else 
        return a;
}
public static long max(long a,long b)
{
    if(a>b)
        return a;
    else
        return b;
}
public static long min(long a,long b)
{
    if(a>b)
        return b;
    else 
        return a;
}

static boolean isPowerOfTwo (long v) {
    return (v & (v - 1)) == 0;
}
public static long pow(long n,long p,long m)
{
     long  result = 1;
      if(p==0)
        return 1;
    if (p==1)
        return n;
    while(p!=0)
    {
        if(p%2==1)
            result *= n;
        if(result>=m)
        result%=m;
        p >>=1;
        n*=n;
        if(n>=m)
        n%=m;
    }
    return result;
}

static class Pair implements Comparable<Pair>
{
    int a,b;
    Pair (int a,int b)
    {
        this.a=a;
        this.b=b;
    }

    public int compareTo(Pair o) {
        // TODO Auto-generated method stub
        if(this.a!=o.a)
        return Integer.compare(this.a,o.a);
        else
            return Integer.compare(this.b, o.b);
        //return 0;
    }
} 
    
static long sort(int a[],int n)
{   int b[]=new int[n]; 
    return mergeSort(a,b,0,n-1);}
static long mergeSort(int a[],int b[],long left,long right)
{ long c=0;if(left<right)
 {   long mid=left+(right-left)/2;
     c= mergeSort(a,b,left,mid);
     c+=mergeSort(a,b,mid+1,right);
     c+=merge(a,b,left,mid+1,right); }  
    return c;    }
static long merge(int a[],int  b[],long left,long mid,long right)
{long c=0;int i=(int)left;int j=(int)mid; int k=(int)left;
while(i<=(int)mid-1&&j<=(int)right)
{ if(a[i]<=a[j]) {b[k++]=a[i++]; }
else    { b[k++]=a[j++];c+=mid-i;}}
while (i <= (int)mid - 1)   b[k++] = a[i++]; 
while (j <= (int)right) b[k++] = a[j++];
for (i=(int)left; i <= (int)right; i++) 
    a[i] = b[i];  return c;  }
    
    
   static  class InputReader
    {
        private InputStream stream;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;
        private SpaceCharFilter filter;

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

        public int read()
        {
            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 int readInt()
        {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            int sgn = 1;
            if (c == '-')
            {
                sgn = -1;
                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 res * sgn;
        }

        public String readString()
        {
            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 double readDouble() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            double res = 0;
            while (!isSpaceChar(c) && c != '.') {
                if (c == 'e' || c == 'E')
                    return res * Math.pow(10, readInt());
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            }
            if (c == '.') {
                c = read();
                double m = 1;
                while (!isSpaceChar(c)) {
                    if (c == 'e' || c == 'E')
                        return res * Math.pow(10, readInt());
                    if (c < '0' || c > '9')
                        throw new InputMismatchException();
                    m /= 10;
                    res += (c - '0') * m;
                    c = read();
                }
            }
            return res * sgn;
        }
        public long readLong() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            int 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 (!isSpaceChar(c));
            return res * sgn;
        }
        public boolean isSpaceChar(int c)
        {
            if (filter != null)
                return filter.isSpaceChar(c);
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }

        public String next()
        {
            return readString();
        }

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

     static class OutputWriter
    {
        private final PrintWriter writer;

        public OutputWriter(OutputStream outputStream)
        {
            writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
        }

        public OutputWriter(Writer writer)
        {
            this.writer = new PrintWriter(writer);
        }

        public void print(Object... objects)
        {
            for (int i = 0; i < objects.length; i++)
            {
                if (i != 0)
                    writer.print(' ');
                writer.print(objects[i]);
            }
        }

        public void printLine(Object... objects)
        {
            print(objects);
            writer.println();
        }

        public void close()
        {
            writer.close();
        }

        public void flush()
        {
            writer.flush();
        }

    }
    /* USAGE

    //initialize
        InputReader in      = new InputReader(System.in);
        OutputWriter out    =   new OutputWriter(System.out);

    //read int
    int i = in.readInt();
    //read string
    String s = in.readString();
    //read int array of size N
    int[] x = IOUtils.readIntArray(in,N);
    //printline
    out.printLine("X");


    //flush output
    out.flush();

    //remember to close the
    //outputstream, at the end
    out.close();

    */
  static   class IOUtils {

        public static int[] readIntArray(InputReader in, int size) {
            int[] array = new int[size];
            for (int i = 0; i < size; i++)
                array[i] = in.readInt();
            return array;
    }
    }
//BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
    //StringBuilder sb=new StringBuilder("");
     //InputReader in = new InputReader(System.in);
  // OutputWriter out = new OutputWriter(System.out);
    //PrintWriter pw=new PrintWriter(System.out);
    //String line=br.readLine().trim();
            
    //int t=Integer.parseInt(br.readLine());
  //    while(t-->0)
    //{
    //int n=Integer.parseInt(br.readLine());
    //long n=Long.parseLong(br.readLine());
    //String l[]=br.readLine().split(" ");
  //int m=Integer.parseInt(l[0]);
    //int k=Integer.parseInt(l[1]);
    //String l[]=br.readLine().split(" ");
    //l=br.readLine().split(" ");
    /*int a[]=new int[n];
    for(int i=0;i<n;i++)
    {
        a[i]=Integer.parseInt(l[i]);
    }*/
       //System.out.println(" ");           
    
    //}
}