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Count ways to N'th Stair(Order does not matter)
Medium Accuracy: 64.12% Submissions: 9208 Points: 4

There are N stairs, and a person standing at the bottom wants to reach the top. The person can climb either 1 stair or 2 stairs at a time. Count the number of ways, the person can reach the top (order does not matter).

Note:
Order does not matter means for n = 4 {1 2 1},{2 1 1},{1 1 2} are considered same.

Example 1:

Input: N = 4
Output: 3
Explanation: Three ways to reach at 4th stair.
They are {1, 1, 1, 1}, {1, 1, 2}, {2, 2}.


Example 2:

Input: N = 5
Output: 3
Explanation: Three ways to reach at 5th stair.
They are {1, 1, 1, 1, 1}, {1, 1, 2, 1} and
{1, 2, 2}.


You don't need to read or print anyhting. Your task is to complete the function nthStair() which takes N as input parameter and returns the total number of ways to reach at Nth stair.

Expected Time Complexity: O(N)
Expected Space Complexity: O(N)

Constraints:
1 ≤ N ≤ 104

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