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.
#整数を変数に格納する場合、変数名=int(input())で格納する。
#文字列を1つの変数に格納する場合、変数名=input()で格納する。
#文字列を複数の変数に格納する場合、変数名A,変数名B,変数名C,変数名D=input()で格納する。
#print(a,b,c,d)⇛a b c d of output
#整数を複数の変数に格納する場合、変数名A,変数名B=map(int,input().split())で格納する。
#文字列を複数の変数に格納する場合、変数名A,変数名B=input().split()で格納する。
#()内にどこで区切るかの情報が入ってる.","とするとカンマ区切りとなる
#List=list(map(int,input().split()))#配列格納
#リスト名=[int(変数名) for 変数名 in input().split()]配列格納
#リストに文字列を格納する場合、リスト名=list(input().split())で格納する。
#a=len(list(set(s)))==2;str sの要素数
#空白区切りの入力で

m1="abcdefghijklmnopqrstuvwxyz"
m2="ABCDEFGHIJKLMNOPQRSTUVWXYZ"
cond=['No','Yes']
Cond=['NO','YES']
#h,w,s=map(int,input().split("/"))#223/333/22
#print(input().count("2"))1121⇛1
#s=s.replace('1','a')1129⇛aa29

n=int(input());
ans=int(n/3);
ans*=2;
ans+=(1 if (n%3)>0 else 0)
print(ans)





