Sum 5
Very easy
Execution time limit is 1 second
Runtime memory usage limit is 64 megabytes
Calculate the sum of the first n terms in the sequence: 1 + 3 + 9 + 27 + 81 ...
Input
A natural number n, where 1 ≤ n ≤ 39.
Output
A single number representing the sum of the first n terms of the sequence.
Examples
Input #1
Answer #1
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