PROGRAMMING:Finding the sum of the first n terms of a fractional sequence

There is a fractional sequence: $$$frac {2} {1}, frac {3} {2}, frac {5} {3}, frac {8} {5}, frac {13} {8}, frac {21} {13} $$. The problem requires the preparation of procedures to find the first N and the sequence.
###Input format:
Keyboard input n (1 $$\ Leq $$n $$\ Leq $$1000)
###Output format:
Sum = s, s is the sum of the first n terms of the sequence, and the result retains four decimal places.
###Input example:
```in
ten
```
###Output example:
```out
sum=16.4799
```







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