import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		StringBuilder sb = new StringBuilder();
		int n = sc.nextInt();
		int[] p = new int[n];
		for (int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}
		int cnt = 0;
		for (int i = 1; i < n - 1; i++) {
			if ((p[i - 1] < p[i] && p[i] < p[i + 1])
					|| (p[i - 1] > p[i] && p[i] > p[i + 1])) {
				cnt++;
			}
		}
		System.out.println(cnt);
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		StringBuilder sb = new StringBuilder();
		int n = sc.nextInt();
		int[] p = new int[n];
		for (int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}
		int cnt = 0;
		for (int i = 1; i < n - 1; i++) {
			if ((p[i - 1] < p[i] && p[i] < p[i + 1])
					|| (p[i - 1] > p[i] && p[i] > p[i + 1])) {
				cnt++;
			}
		}
		System.out.println(cnt);
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		StringBuilder sb = new StringBuilder();
		int n = sc.nextInt();
		int[] p = new int[n];
		for (int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}
		int cnt = 0;
		for (int i = 1; i < n - 1; i++) {
			if ((p[i - 1] < p[i] && p[i] < p[i + 1])
					|| (p[i - 1] > p[i] && p[i] > p[i + 1])) {
				cnt++;
			}
		}
		System.out.println(cnt);
	} main {
		Scanner sc = new Scanner(System.in);
		StringBuilder sb = new StringBuilder();
		int n = sc.nextInt();
		int[] p = new int[n];
		for (int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}
		int cnt = 0;
		for (int i = 1; i < n - 1; i++) {
			if ((p[i - 1] < p[i] && p[i] < p[i + 1])
					|| (p[i - 1] > p[i] && p[i] > p[i + 1])) {
				cnt++;
			}
		}
		System.out.println(cnt);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) StringBuilder sb = new StringBuilder(); sb new StringBuilder() int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int[] p = new int[n]; p new int[n] n for (int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		} int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
			p[i] = sc.nextInt();
		} {
			p[i] = sc.nextInt();
		} p[i] = sc.nextInt() p[i] p i sc.nextInt() sc.nextInt sc int cnt = 0; cnt 0 for (int i = 1; i < n - 1; i++) {
			if ((p[i - 1] < p[i] && p[i] < p[i + 1])
					|| (p[i - 1] > p[i] && p[i] > p[i + 1])) {
				cnt++;
			}
		} int i = 1; int i = 1; i 1 i < n - 1 i n - 1 n 1 i++ i++ i {
			if ((p[i - 1] < p[i] && p[i] < p[i + 1])
					|| (p[i - 1] > p[i] && p[i] > p[i + 1])) {
				cnt++;
			}
		} {
			if ((p[i - 1] < p[i] && p[i] < p[i + 1])
					|| (p[i - 1] > p[i] && p[i] > p[i + 1])) {
				cnt++;
			}
		} if ((p[i - 1] < p[i] && p[i] < p[i + 1])
					|| (p[i - 1] > p[i] && p[i] > p[i + 1])) {
				cnt++;
			} (p[i - 1] < p[i] && p[i] < p[i + 1])
					|| (p[i - 1] > p[i] && p[i] > p[i + 1]) (p[i - 1] < p[i] && p[i] < p[i + 1]) p[i - 1] < p[i] p[i - 1] p i - 1 i 1 p[i] p i p[i] < p[i + 1] p[i] p i p[i + 1] p i + 1 i 1 (p[i - 1] > p[i] && p[i] > p[i + 1]) p[i - 1] > p[i] p[i - 1] p i - 1 i 1 p[i] p i p[i] > p[i + 1] p[i] p i p[i + 1] p i + 1 i 1 {
				cnt++;
			} cnt++ cnt System.out.println(cnt) System.out.println System.out System System.out cnt String[] args args public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		StringBuilder sb = new StringBuilder();
		int n = sc.nextInt();
		int[] p = new int[n];
		for (int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}
		int cnt = 0;
		for (int i = 1; i < n - 1; i++) {
			if ((p[i - 1] < p[i] && p[i] < p[i + 1])
					|| (p[i - 1] > p[i] && p[i] > p[i + 1])) {
				cnt++;
			}
		}
		System.out.println(cnt);
	}
} public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		StringBuilder sb = new StringBuilder();
		int n = sc.nextInt();
		int[] p = new int[n];
		for (int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}
		int cnt = 0;
		for (int i = 1; i < n - 1; i++) {
			if ((p[i - 1] < p[i] && p[i] < p[i + 1])
					|| (p[i - 1] > p[i] && p[i] > p[i + 1])) {
				cnt++;
			}
		}
		System.out.println(cnt);
	}
} Main
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		StringBuilder sb = new StringBuilder();
		int n = sc.nextInt();
		int[] p = new int[n];
		for (int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}
		int cnt = 0;
		for (int i = 1; i < n - 1; i++) {
			if ((p[i - 1] < p[i] && p[i] < p[i + 1])
					|| (p[i - 1] > p[i] && p[i] > p[i + 1])) {
				cnt++;
			}
		}
		System.out.println(cnt);
	}
}
