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

public class Solution {

    private void solution() throws IOException {
        int a = in.nextInt();
        out.println(solve(a));
//      int sum = 0;
//      String number = "";
//      for (int i = 1; i < 100000; ++i) {
//          number += i;
//          if (((new BigInteger(number)).mod(BigInteger.valueOf(3)).equals(BigInteger.ZERO))) {
//              ++sum;
//          }
//          if (sum != solve(i)) {
//              out.println("for i = " + i + " ans = { " + sum + "->" + solve(i) + " }");
////                out.println(i + " " + sum + " " + number);
//          }
//      }
        out.flush();
    }

    private int solve(int a) {
        if (a == 1) {
            return 0;
        }
        int mod = (a - 2) % 3;
        if (mod == 0) {
            return get(a);
        }
        int left = a - mod;
        return get(left) + 1;
    }

    private int get(int a) {
        return ((a - 2) / 3) * 2 + 1;
    }

    private class Scanner {
        BufferedReader reader;
        StringTokenizer tokenizer;

        public Scanner(Reader reader) {
            this.reader = new BufferedReader(reader);
            this.tokenizer = new StringTokenizer("");
        }

        public boolean hasNext() throws IOException {
            while (!tokenizer.hasMoreTokens()) {
                String next = reader.readLine();
                if (next == null) {
                    return false;
                }
                tokenizer = new StringTokenizer(next);
            }
            return true;
        }

        public String next() throws IOException {
            hasNext();
            return tokenizer.nextToken();
        }

        public int nextInt() throws IOException {
            return Integer.parseInt(next());
        }

        public String nextLine() throws IOException {
            tokenizer = new StringTokenizer("");
            return reader.readLine();
        }
    }

    public static void main(String[] args) throws IOException {
        (new Solution()).solution();
    }

    PrintWriter out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));
    Scanner in = new Scanner(new InputStreamReader(System.in));
}