PROGRAMMING:Calculate 21 + 22 + 23 +... + M

Enter a positive integer m (30 < = m < = 100) to calculate the value of the expression 21 + 22 + 23 +... + M.
###Input format:
Enter a positive integer m on one line
###Output format:
In one line, output the corresponding sum and s in the format "sum = s"
###Input example:
Here is a set of inputs. For example:
```in
ninety
```
###Output example:
The corresponding output is given here. For example:
```out
sum = 3885
```







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