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?
The only line of the input contains a single integer *n* (1 ≤ *n* ≤ 10<sup class="upper-index">9</sup>) — number of stones Artem received on his birthday.
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.
1
1
2
1
3
2
4
3
100
67
101
67
102
68
1000000000
666666667
5
3
6
4
999999999
666666666
999999998
666666665
999999997
666666665
999999996
666666664
999999995
666666663
999999994
666666663
999999993
666666662
999999992
666666661
999999991
666666661
1000
667
10000
6667
100000
66667
1000000
666667
10000000
6666667
100000000
66666667
7
5
n=int(input("enter the number of stones "))
if n== 1:
    print(n-0)
elif n!=1:
    print(n-1)