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 static java.lang.Math.*;

import java.io.DataInputStream; 
import java.io.FileInputStream; 
import java.io.IOException; 
import java.io.InputStreamReader;
import java.io.PrintStream;
import java.io.PrintWriter;
import java.math.BigInteger; 

public class Main 
{ 

	static int mod = 1000000007;
	static int MOD = 1000000007;
	static final long M = (int)1e9+7;

	
	static class Pair implements Comparable<Pair>
	{
		int first, second;
		public Pair(int aa, int bb)
		{
			first = aa; second = bb;
		}
		public int compareTo(Pair p)
		{
//			if(a == p.a) return b - p.b;
//			return a - p.a;
			if(first == p.first) return second - p.second;
			return first - p.first;
		}
	}
	
	/*
	 * IO FOR 2D GRID IN JAVA
	 * char[][] arr = new char[n][m]; //grid in Q.
			
			for(int i = 0;i<n;i++)
			{
				char[] nowLine = sc.next().toCharArray();
				for(int j = 0;j<m;j++)
				{
					arr[i][j] = nowLine[i];
				}
			}
	 * */
	
	static class Reader 
	{ 
		final private int BUFFER_SIZE = 1 << 16; 
		private DataInputStream din; 
		private byte[] buffer; 
		private int bufferPointer, bytesRead; 

		public Reader() 
		{ 
			din = new DataInputStream(System.in); 
			buffer = new byte[BUFFER_SIZE]; 
			bufferPointer = bytesRead = 0; 
		} 

		public Reader(String file_name) throws IOException 
		{ 
			din = new DataInputStream(new FileInputStream(file_name)); 
			buffer = new byte[BUFFER_SIZE]; 
			bufferPointer = bytesRead = 0; 
		} 

		public String next() throws IOException 
		{ 
			byte[] buf = new byte[64]; // line length 
			int cnt = 0, c; 
			while ((c = read()) != -1) 
			{ 
				if (c == '\n') 
					break; 
				buf[cnt++] = (byte) c; 
			} 
			return new String(buf, 0, cnt); 
		} 
		
		public int nextInt() throws IOException 
		{ 
			int ret = 0; 
			byte c = read(); 
			while (c <= ' ') 
				c = read(); 
			boolean neg = (c == '-'); 
			if (neg) 
				c = read(); 
			do
			{ 
				ret = ret * 10 + c - '0'; 
			} while ((c = read()) >= '0' && c <= '9'); 

			if (neg) 
				return -ret; 
			return ret; 
		}
		int[] readArray(int n) throws IOException {
			int[] a=new int[n];
			for (int i=0; i<n; i++) a[i]=nextInt();
			return a;
		}

		public long nextLong() throws IOException 
		{ 
			long ret = 0; 
			byte c = read(); 
			while (c <= ' ') 
				c = read(); 
			boolean neg = (c == '-'); 
			if (neg) 
				c = read(); 
			do { 
				ret = ret * 10 + c - '0'; 
			} 
			while ((c = read()) >= '0' && c <= '9'); 
			if (neg) 
				return -ret; 
			return ret; 
		} 

		public double nextDouble() throws IOException 
		{ 
			double ret = 0, div = 1; 
			byte c = read(); 
			while (c <= ' ') 
				c = read(); 
			boolean neg = (c == '-'); 
			if (neg) 
				c = read(); 

			do { 
				ret = ret * 10 + c - '0'; 
			} 
			while ((c = read()) >= '0' && c <= '9'); 

			if (c == '.') 
			{ 
				while ((c = read()) >= '0' && c <= '9') 
				{ 
					ret += (c - '0') / (div *= 10); 
				} 
			} 

			if (neg) 
				return -ret; 
			return ret; 
		} 

		private void fillBuffer() throws IOException 
		{ 
			bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE); 
			if (bytesRead == -1) 
				buffer[0] = -1; 
		} 

		private byte read() throws IOException 
		{ 
			if (bufferPointer == bytesRead) 
				fillBuffer(); 
			return buffer[bufferPointer++]; 
		} 

		public void close() throws IOException 
		{ 
			if (din == null) 
				return; 
			din.close(); 
		}

		public BigInteger nextBigInteger() {
			// TODO Auto-generated method stub
			return null;
		}

	}

	
	public static boolean isPrime(int n) {
		if(n == 1)
		{
			return false;
		}
		for(int i = 2;i*i<=n;i++)
		{
			if(n%i == 0)
			{
				return false;
			}
		}
		return true;
	}
	
	public static ArrayList<Integer> sieveList(int n)
	{
	       
		ArrayList<Integer> list = new ArrayList<>();
	    boolean prime[]=new boolean[n+2];
	    for(int i=0;i<(n+1);i++)
	    {
	        prime[i]=true;
	    }
	    for(int i=2;i*i<=(n+1);i++)
	    {
	        if(prime[i]==true)
	        for(int p=i*2;p<=(n+1);p+=i)
	        prime[p]=false;
	    }
	    for(int i=2;i<=(n+1);i++)
	    {
	        if(prime[i]==true)
	        list.add(i);
	    }
	    return list;
}
	
	public static int gcd(int a, int b)
	{
		if(b == 0)
		 return a;
		
		else
		return gcd(b,a%b);
	}
	
	public static long LongGCD(long a, long b)
	{
		if(b == 0)
			 return a;
			
			else
			return LongGCD(b,a%b);
	}


	public static int lcm(int a, int b)
    {
        return (a / gcd(a, b)) * b;
    }
	
	public static int phi(int n)  //euler totient function
    { 
        int result = 1; 
        for (int i = 2; i < n; i++) 
            if (gcd(i, n) == 1) 
                result++; 
        return result; 
    }
	
	
	public static int[] computePrefix(int arr[], int n)
	{
		int[] prefix = new int[n];
		prefix[0] = arr[0];
		for(int i = 1;i<n;i++)
		{
			prefix[i] = prefix[i-1]+arr[i];
		}
		
		return prefix;
	}
	
	
	public static int fastPow(int x, int n) //include mod at each step if asked and in args of fn too
	{
		if(n == 0)
			return 1;
		else if(n%2 == 0)
			return fastPow(x*x,n/2);
		else
			return x*fastPow(x*x,(n-1)/2);
	}
	
	
	   static int power(int x, int y, int p)
	    {
	 
	        int res = 1;
	 
	        x = x % p;
	 
	        while (y > 0) {
	            if (y % 2 == 1)
	                res = (res * x) % p;
	 
	            y = y >> 1; 
	            x = (x * x) % p;
	        }
	 
	        return res;
	    }
	 
	    static int modInverse(int n, int p)
	    {
	        return power(n, p - 2, p);
	    }
	    
	    //Fermat's little theorem for nCr % p.
	    static int nCrModPFermat(int n, int r,
	                             int p)
	    {
	 
	          if (n<r) 
	              return 0;
	        if (r == 0)
	            return 1;
	        int[] fac = new int[n + 1];
	        fac[0] = 1;
	 
	        for (int i = 1; i <= n; i++)
	            fac[i] = fac[i - 1] * i % p;
	 
	        return (fac[n] * modInverse(fac[r], p)
	                % p * modInverse(fac[n - r], p)
	                % p)
	            % p;
	    }
	    

		static int LowerBound(int a[], int x) {
			  int l=-1,r=a.length;
			  while(l+1<r) {
			    int m=(l+r)>>>1;
			    if(a[m]>=x) r=m;
			    else l=m;
			  }
			  return r;
			}
		
		
		static int UpperBound(int a[], int x) {
		    int l=-1,r=a.length;
		    while(l+1<r) {
		       int m=(l+r)>>>1;
		       if(a[m]<=x) l=m;
		       else r=m;
		    }
		    return l+1;
		 }
		
	    
	    
		public static void Sort(int[] a) {
			List<Integer> l=new ArrayList<>();
			for (int i:a) l.add(i);
			Collections.sort(l);
			//Collections.reverse(l);  //Use to Sort decreasingly 
			for (int i=0; i<a.length; i++) a[i]=l.get(i);
		}
	

		public static void main(String[] args) throws IOException 
		{ 
			Reader sc = new Reader();
			PrintWriter out = new PrintWriter(System.out);
			
			long n = sc.nextLong();
			
			if(n%2 != 0)
			{
				System.out.println(0);
				return;
			}
			n/=2;
			long ans = n-1;
			if(n%2 == 0) n--;
			
			System.out.println((ans/2));
			
			out.close();
		}
}


 