PROGRAMMING:Sum of powers
This problem requires the preparation of procedures to calculate $$sum = 2 ^ 1 + 2 ^ 2 + 2 ^ 3 + - cdots + 2 ^ n $$. The pow function can be called for exponentiation.
###Input format:
Input gives a positive integer $$n $$($$Le $$10) on one line.
###Output format:
Output according to the format "result = calculation result".
###Input example:
```in
five
```
###Output example:
```out
result = 62
```
answer：If there is no answer, please comment
###Input format:
Input gives a positive integer $$n $$($$Le $$10) on one line.
###Output format:
Output according to the format "result = calculation result".
###Input example:
```in
five
```
###Output example:
```out
result = 62
```
answer：If there is no answer, please comment