Description

There is a kind of bacterium(細菌) and its life is 3 week.

At end of first week, it divides into 2 bacteria.

At end of second week, it divides into 2 bacteria again.

At third week, it does nothing and die.

For example, we have one bacterium at first week.

At begin of 5^th week, there are total 10 bacteria.

Now, give you week W. You should tell me how many bacterium at begin of W^th week.

Input

One integer, week W.

1<= W <=40

Output

How much bacterium at begin of W^th week.

Sample Input  Download

Sample Output  Download

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