Little Artem got n stones on his birthday and now wants to give some of them to Masha. He knows that Masha cares more about the fact of receiving the present, rather than the value of that present, so he wants to give her stones as many times as possible. However, Masha remembers the last present she received, so Artem can't give her the same number of stones twice in a row. For example, he can give her 3 stones, then 1 stone, then again 3 stones, but he can't give her 3 stones and then again 3 stones right after that.

How many times can Artem give presents to Masha?

Input

The only line of the input contains a single integer n (1 ≤ n ≤ 109) — number of stones Artem received on his birthday.

Output

Print the maximum possible number of times Artem can give presents to Masha.

Examples

Input

1


Output

1


Input

2


Output

1


Input

3


Output

2


Input

4


Output

3

Note

In the first sample, Artem can only give 1 stone to Masha.

In the second sample, Atrem can give Masha 1 or 2 stones, though he can't give her 1 stone two times.

In the third sample, Atrem can first give Masha 2 stones, a then 1 more stone.

In the fourth sample, Atrem can first give Masha 1 stone, then 2 stones, and finally 1 stone again.

import java.io.*;
import java.util.*;
/**
 *
 * @author Sourav Kumar Paul (spaul100)
 * NIT Silchar    
 */

public class SolveA {

    public static Reader in;
    public static PrintWriter out;
    public static long mod = 1000000007;
    public static long inf = 100000000000000000l;
    public static long fac[],inv[];
    public static int union[];

    public static void solve(){
        int n = in.nextInt();
        int x = n/3;
        long count = x*2;
        if(n%3!=0)
            count++;
        out.println(count);
    }

/**
 *  ############################### Template ################################
 */
    

    public static class Pair implements Comparable{
        int x,y;
       
        Pair(int x, int y)
        {
            this.x = x;
            this.y = y;
        }
        @Override
        public int compareTo(Object o)
        {
            Pair pp = (Pair)o;
            if(pp.x == x)
                return 0;
            else if (x>pp.x)
                return 1;
            else 
                return -1;
        }
    }

   
    public static void init()
    {
        for(int i=0; i<union.length; i++)
            union[i] = i;
    }
    public static int find(int n)
    {
        return (union[n]==n)?n:(union[n]=find(union[n]));
    }
    public static void unionSet(int i ,int j)
    {
        union[find(i)]=find(j);
    }
    public static boolean connected(int i,int j)
    {   
        return union[i]==union[j];
    }

    public static long gcd(long a, long b) {
        long x = Math.min(a,b);
        long y = Math.max(a,b);
        while(x!=0)
        {
            long temp = x;
            x = y%x;
            y = temp;
        }
        return y;       
    }

    public static long modPow(long base, long exp, long mod) {
        base = base % mod;
        long result =1;
        while(exp > 0)
        {
            if(exp % 2== 1)
            {
                result = (result * base) % mod;
                exp --;
            }
            else
            {
                base = (base * base) % mod;
                exp = exp >> 1;
            }
            
        }
        return result;
    }
    
    public static void cal()
    {
        fac = new long[1000005];
        inv = new long[1000005];
        fac[0]=1;
        inv[0]=1;
        for(int i=1; i<=1000000; i++)
        {
            fac[i]=(fac[i-1]*i)%mod;
            inv[i]=(inv[i-1]*modPow(i,mod-2,mod))%mod;
        }
    }
    public static long ncr(int n, int r)
    {
        return (((fac[n]*inv[r])%mod)*inv[n-r])%mod;
    }


    SolveA() throws IOException {
	in = new Reader(new InputStreamReader(System.in));
        out = new PrintWriter(new OutputStreamWriter(System.out));
	solve();
        out.flush();
	out.close();
    }
 
    public static void main(String args[]) {
	new Thread(null, new Runnable() {
            public void run() {
                try {
                    new SolveA();
		} catch (Exception e) {
                    e.printStackTrace();
		}
            }
	}, "1", 1 << 26).start();
    }
    
    public static class Reader {
        public BufferedReader reader;
        public StringTokenizer st;

        public Reader(InputStreamReader stream) {
            reader = new BufferedReader(stream);
            st = null;
        }

        public String next() {
            while (st == null || !st.hasMoreTokens()) {
                try {
                    st = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return st.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }
        public String nextLine() throws IOException{
            return reader.readLine();
        }
        public long nextLong(){
            return Long.parseLong(next());
        }
        public double nextDouble(){
            return Double.parseDouble(next());
        }

    }
}

