Count Descending Subarrays

Count only contiguous subarrays of length at least 2 in which every adjacent element decreases by exactly 1.

输入格式

The first line contains n, and the second line contains the integers. The source only gives n≥1; on this site n≤200000 and −10^9≤element≤10^9.

输出格式

Output one integer, the answer.

样例 1

输入：

5
7 6 5 5 4

输出：

4

样例 2

输入：

4
4 3 2 1

输出：

6

样例 3

输入：

1
9

输出：

0

样例说明

The examples give 4, 6 and 0 respectively.