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C. Lucky Numbers

time limit per test

0.5 secondsmemory limit per test

64 megabytesinput

standard inputoutput

standard outputThe numbers of all offices in the new building of the Tax Office of IT City will have lucky numbers.

Lucky number is a number that consists of digits 7 and 8 only. Find the maximum number of offices in the new building of the Tax Office given that a door-plate can hold a number not longer than *n* digits.

Input

The only line of input contains one integer *n* (1 ≤ *n* ≤ 55) — the maximum length of a number that a door-plate can hold.

Output

Output one integer — the maximum number of offices, than can have unique lucky numbers not longer than *n* digits.

Examples

Input

2

Output

6

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