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.
T_ON = 0
DEBUG_ON = 1
MOD = 998244353


def solve():
    n = read_int()
    q, r = divmod(n, 3)
    total = 2 * q
    if r:
        total += 1
    print(total)


def main():
    T = read_int() if T_ON else 1
    for i in range(T):
        solve()


def debug(*xargs):
    if DEBUG_ON:
        print(*xargs)


from collections import *
import math


#---------------------------------FAST_IO---------------------------------------

import os
import sys
from io import BytesIO, IOBase
# region fastio

BUFSIZE = 8192


class FastIO(IOBase):
    newlines = 0

    def __init__(self, file):
        self._fd = file.fileno()
        self.buffer = BytesIO()
        self.writable = "x" in file.mode or "r" not in file.mode
        self.write = self.buffer.write if self.writable else None

    def read(self):
        while True:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
            if not b:
                break
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines = 0
        return self.buffer.read()

    def readline(self):
        while self.newlines == 0:
            b = os.read(self._fd, max(os.fstat(self._fd).st_size, BUFSIZE))
            self.newlines = b.count(b"\n") + (not b)
            ptr = self.buffer.tell()
            self.buffer.seek(0, 2), self.buffer.write(b), self.buffer.seek(ptr)
        self.newlines -= 1
        return self.buffer.readline()

    def flush(self):
        if self.writable:
            os.write(self._fd, self.buffer.getvalue())
            self.buffer.truncate(0), self.buffer.seek(0)


class IOWrapper(IOBase):
    def __init__(self, file):
        self.buffer = FastIO(file)
        self.flush = self.buffer.flush
        self.writable = self.buffer.writable
        self.write = lambda s: self.buffer.write(s.encode("ascii"))
        self.read = lambda: self.buffer.read().decode("ascii")
        self.readline = lambda: self.buffer.readline().decode("ascii")


sys.stdin, sys.stdout = IOWrapper(sys.stdin), IOWrapper(sys.stdout)
input = lambda: sys.stdin.readline().rstrip("\r\n")

#----------------------------------IO_WRAP--------------------------------------

def read_int():
    return int(input())


def read_ints():
    return list(map(int, input().split()))


def print_nums(nums):
    print(" ".join(map(str, nums)))


def YES():
    print("YES")


def Yes():
    print("Yes")


def NO():
    print("NO")


def No():
    print("No")


def First():
    print("First")


def Second():
    print("Second")


#----------------------------------FIB--------------------------------------

def fib(n):
    a, b = 0, 1
    for _ in range(n):
        a, b = b, a + b
    return a


def fib_ns(n):
    assert n >= 1
    f = [0 for _ in range(n + 1)]
    f[0] = 0
    f[1] = 1
    for i in range(2, n + 1):
        f[i] = f[i - 1] + f[i - 2]
    return f

#----------------------------------MOD--------------------------------------

def gcd(a, b):
    if a == 0:
        return b
    return gcd(b % a, a)


def xgcd(a, b):
    """return (g, x, y) such that a*x + b*y = g = gcd(a, b)"""
    x0, x1, y0, y1 = 0, 1, 1, 0
    while a != 0:
        (q, a), b = divmod(b, a), a
        y0, y1 = y1, y0 - q * y1
        x0, x1 = x1, x0 - q * x1
    return b, x0, y0


def lcm(a, b):
    d = gcd(a, b)
    return a * b // d


def is_even(x):
    return x % 2 == 0


def is_odd(x):
    return x % 2 == 1


def modinv(a, m):
    """return x such that (a * x) % m == 1"""
    g, x, _ = xgcd(a, m)
    if g != 1:
        raise Exception('gcd(a, m) != 1')
    return x % m


def mod_add(x, y):
    x += y
    while x >= MOD:
        x -= MOD
    while x < 0:
        x += MOD
    return x


def mod_mul(x, y):
    return (x * y) % MOD


def mod_pow(x, y):
    if y == 0:
        return 1
    if y % 2:
        return mod_mul(x, mod_pow(x, y - 1))
    p = mod_pow(x, y // 2)
    return mod_mul(p, p)


def mod_inv(y):
    return mod_pow(y, MOD - 2)


def mod_div(x, y):
    # y^(-1): Fermat little theorem, MOD is a prime
    return mod_mul(x, mod_inv(y))

#---------------------------------PRIME---------------------------------------

def is_prime(n):
    if n == 1:
        return False
    for i in range(2, int(n ** 0.5) + 1):
        if n % i:
            return False
    return True


def gen_primes(n):
    """
    generate primes of [1..n] using sieve's method
    """
    P = [True for _ in range(n + 1)]
    P[0] = P[1] = False
    for i in range(int(n ** 0.5) + 1):
        if P[i]:
            for j in range(2 * i, n + 1, i):
                P[j] = False
    return P

#---------------------------------MAIN---------------------------------------

main()
