PROGRAMMING:Finding the sum of fractional sequences
###Task description
There is a fractional sequence 2 / 1,3 / 2,5 / 3,8 / 5,13 / 8,21 / 13,.... find the sum of the first n terms of this fractional sequence.
###Input format:
The input has one line: positive integer n.
###Output format:
The output has one line: the sum of the fractional sequence (floating point number, accurate to 4 decimal places).
###Input example:
```in
ninety-nine
```
###Output example:
```out
one hundred and sixty point four eight four nine
```
###Tips
It is better to use double precision floating-point number (double) record in the program to get the sum.
###Title Source
Note: selected from openjudge website, online address: http://sdau.openjudge.cn/c/007/ .
###Problem analysis
The content of Fibonacci sequence is: 1,1,2,3,5,8,13,21,34,55... The rule starts with two ones, and the latter is the sum of the former two.
The fractional sequence of this problem is actually the sum of the ratio of the last term to the previous term of Fibonacci sequence starting from 1,2,3,4,5. The key of the problem is to find the sum of the nth term of Fibonacci sequence.
Please note that the variables F1, F2 and F3 used to save the Fibonacci sequence items in the program code will overflow if they are defined as integers, because the later the sequence is, the larger the value is.
answer：If there is no answer, please comment
There is a fractional sequence 2 / 1,3 / 2,5 / 3,8 / 5,13 / 8,21 / 13,.... find the sum of the first n terms of this fractional sequence.
###Input format:
The input has one line: positive integer n.
###Output format:
The output has one line: the sum of the fractional sequence (floating point number, accurate to 4 decimal places).
###Input example:
```in
ninety-nine
```
###Output example:
```out
one hundred and sixty point four eight four nine
```
###Tips
It is better to use double precision floating-point number (double) record in the program to get the sum.
###Title Source
Note: selected from openjudge website, online address: http://sdau.openjudge.cn/c/007/ .
###Problem analysis
The content of Fibonacci sequence is: 1,1,2,3,5,8,13,21,34,55... The rule starts with two ones, and the latter is the sum of the former two.
The fractional sequence of this problem is actually the sum of the ratio of the last term to the previous term of Fibonacci sequence starting from 1,2,3,4,5. The key of the problem is to find the sum of the nth term of Fibonacci sequence.
Please note that the variables F1, F2 and F3 used to save the Fibonacci sequence items in the program code will overflow if they are defined as integers, because the later the sequence is, the larger the value is.
answer：If there is no answer, please comment