101321: [AtCoder]ABC132 B - Ordinary Number
Memory Limit:256 MB
Time Limit:2 S
Judge Style:Text Compare
Creator:
Submit:0
Solved:0
Description
Score : $200$ points
Problem Statement
We have a permutation $p$ = {$p_1,\ p_2,\ ...,\ p_n$} of {$1,\ 2,\ ...,\ n$}.
Print the number of elements $p_i$ ($1 < i < n$) that satisfy the following condition:
- $p_i$ is the second smallest number among the three numbers $p_{i - 1}$, $p_i$, and $p_{i + 1}$.
Constraints
- All values in input are integers.
- $3 \leq n \leq 20$
- $p$ is a permutation of {$1,\ 2,\ ...,\ n$}.
Input
Input is given from Standard Input in the following format:
$n$ $p_1$ $p_2$ $...$ $p_n$
Output
Print the number of elements $p_i$ ($1 < i < n$) that satisfy the condition.
Sample Input 1
5 1 3 5 4 2
Sample Output 1
2
$p_2 = 3$ is the second smallest number among $p_1 = 1$, $p_2 = 3$, and $p_3 = 5$. Also, $p_4 = 4$ is the second smallest number among $p_3 = 5$, $p_4 = 4$, and $p_5 = 2$. These two elements satisfy the condition.
Sample Input 2
9 9 6 3 2 5 8 7 4 1
Sample Output 2
5