PROGRAMMING:Finding the sum of the first n terms of fractional sequence
This problem requires programming to calculate the sum of the first n items of the sequence 2 / 1 + 3 / 2 + 5 / 3 + 8 / 5 +. Note that the sequence starts from item 2. The numerator of each item is the sum of the numerator of the previous item and the denominator, and the denominator is the numerator of the previous item.
###Input format:
The input gives a positive integer n on one line.
###Output format:
Output the value of partial sum in one line, accurate to two decimal places. The calculation results should not exceed the double precision range.
###Input example:
```in
twenty
```
###Output example:
```out
thirty-two point six six
```
answer：If there is no answer, please comment
###Input format:
The input gives a positive integer n on one line.
###Output format:
Output the value of partial sum in one line, accurate to two decimal places. The calculation results should not exceed the double precision range.
###Input example:
```in
twenty
```
###Output example:
```out
thirty-two point six six
```
answer：If there is no answer, please comment