1. Description

Let's define a sequence of integers:

• The 0-th item is 1, the 1-st element is 2
• For any of the following item, it equals t o sum of previous two elements and then minus 1

Code a function fibo, which takes an integer n as input and returns the n-th item of this sequence

2. Input & Output

Input:

• An integer
• Use input() as input. Notice that the value you get from input() is a string

Output:

• An integer
• Use print() for your output

Example

# Input: 
0
# Output: 
1

# Input: 
2
# Output: 
2