You are given an integer array `prices` representing the daily price history of a stock, where `prices[i]` is the stock price on the `ith` day.

A smooth descent period of a stock consists of one or more contiguous days such that the price on each day is lower than the price on the preceding day by exactly `1`. The first day of the period is exempted from this rule.

Return the number of smooth descent periods.

Example 1:

    Input: prices = [3,2,1,4]
    Output: 7
    Explanation: There are 7 smooth descent periods:
    [3], [2], [1], [4], [3,2], [2,1], and [3,2,1]
    Note that a period with one day is a smooth descent period by the definition.

Example 2:

    Input: prices = [8,6,7,7]
    Output: 4
    Explanation: There are 4 smooth descent periods: [8], [6], [7], and [7]
    Note that [8,6] is not a smooth descent period as 8 - 6 ≠ 1.

Example 3:

    Input: prices = [1]
    Output: 1
    Explanation: There is 1 smooth descent period: [1]

Constraints:

- `1 <= prices.length <= 105`
- `1 <= prices[i] <= 105`