Pancake

In your house, the family takes turns preparing breakfast. Today you are going to make pancakes. The pancakes will cook on one side in one minute. If you cook both sides, they are ready. You have a frying pan. With this pan, you can cook up to three pancakes at a time, but only on one side.

Write a program which reads the number of pancakes and finds the minimum time (in minutes) required to make all the pancakes.

Input

The input is given in the following format

$N$

The number of pancakes $N$ ($1 \leq N \leq 1,000$) is given as an integer in a line.

Output

Output the minimum time required to make all the pancakes in a line.

Sample Input and Output

Sample Input 1

3

Sample Output 1

2

Sample Input 2

4

Sample Output 2

3

In Sample Input 2, let the pancakes be A, B, C, and D. First, you cook the front sides of A, B, C. Then you cook the back sides of A and B, and the front side of D. Finally, you cook the back side of C and D. In this way, you can cook all in 3 minutes.  

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