You are climbing a staircase with n steps. Each time you can climb 1 or 2 steps. In how many distinct ways can you climb to the top?

• An integer n.

• 1 <= n <= 45

Input: n = 5
Output: 8
Explanation: (1+1+1+1+1), (1+1+1+2), (1+1+2+1), (1+2+1+1), (2+1+1+1), (1+2+2), (2+1+2), (2+2+1).