use std::io;

fn main() {
    io::stdin().read_line(&mut String::new()).ok();
    let mut aa = String::new();
    io::stdin().read_line(&mut aa).ok();
    let aa = aa
        .split_whitespace()
        .map(|n| n.parse::<u64>().unwrap())
        .collect::<Vec<_>>();

    let answer = aa
        .windows(3)
        .filter(|&x| {
            x[1] < x[0] && x[0] < x[2]
                || x[1] > x[0] && x[0] > x[2]
                || x[1] < x[2] && x[2] < x[0]
                || x[1] > x[2] && x[2] > x[0]
        })
        .count();

    println!("{}", answer);
}