You are given an integer array `cost` where `cost[i]` is the cost of `ith` step on a staircase. Once you pay the cost, you can either climb one or two steps.

You can either start from the step with index `0`, or the step with index `1`.

Return the minimum cost to reach the top of the floor.

Example 1:

    Input: cost = [10,15,20]
    Output: 15
    Explanation: You will start at index 1.
    - Pay 15 and climb two steps to reach the top.
    The total cost is 15.

Example 2:

    Input: cost = [1,100,1,1,1,100,1,1,100,1]
    Output: 6
    Explanation: You will start at index 0.
    - Pay 1 and climb two steps to reach index 2.
    - Pay 1 and climb two steps to reach index 4.
    - Pay 1 and climb two steps to reach index 6.
    - Pay 1 and climb one step to reach index 7.
    - Pay 1 and climb two steps to reach index 9.
    - Pay 1 and climb one step to reach the top.
    The total cost is 6.

Constraints:

- `2 <= cost.length <= 1000`
- `0 <= cost[i] <= 999`