PROGRAMMING:Rabbit jumping stairs

Bunny likes to jump up stairs. He can jump up one or two stairs at a time. Ask little rabbit how many different ways to go up an n-step staircase?
###Input format:
The input line contains an integer n to indicate how many stairs there are.
###Output format:
How to go up stairs
###Input example:
```in
three
```
###Output example:
```out
three
```
###Scale and convention of evaluation case
For 20% of the evaluation cases, 1 ≤ n ≤ 10.
For 50% of the evaluation cases, 1 ≤ n ≤ 100.
For 80% of the evaluation cases, 1 ≤ n ≤ 1000.
For all evaluation cases, 1 ≤ n ≤ 10000< br>





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