import java.util.Arrays;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();
		int[] p = new int[n];
		int res = 0;

		for (int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}
		for (int i = 1; i < n - 1; i++) {
			int[] a = { p[i - 1], p[i], p[i + 1] };
			Arrays.sort(a);
			if (a[1] == p[i]) {
				res++;
			}
		}

		System.out.println(res);
	}
} import java.util.Arrays; Arrays java.util import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();
		int[] p = new int[n];
		int res = 0;

		for (int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}
		for (int i = 1; i < n - 1; i++) {
			int[] a = { p[i - 1], p[i], p[i + 1] };
			Arrays.sort(a);
			if (a[1] == p[i]) {
				res++;
			}
		}

		System.out.println(res);
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();
		int[] p = new int[n];
		int res = 0;

		for (int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}
		for (int i = 1; i < n - 1; i++) {
			int[] a = { p[i - 1], p[i], p[i + 1] };
			Arrays.sort(a);
			if (a[1] == p[i]) {
				res++;
			}
		}

		System.out.println(res);
	} main {
		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();
		int[] p = new int[n];
		int res = 0;

		for (int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}
		for (int i = 1; i < n - 1; i++) {
			int[] a = { p[i - 1], p[i], p[i + 1] };
			Arrays.sort(a);
			if (a[1] == p[i]) {
				res++;
			}
		}

		System.out.println(res);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int[] p = new int[n]; p new int[n] n int res = 0; res 0 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 for (int i = 1; i < n - 1; i++) {
			int[] a = { p[i - 1], p[i], p[i + 1] };
			Arrays.sort(a);
			if (a[1] == p[i]) {
				res++;
			}
		} int i = 1; int i = 1; i 1 i < n - 1 i n - 1 n 1 i++ i++ i {
			int[] a = { p[i - 1], p[i], p[i + 1] };
			Arrays.sort(a);
			if (a[1] == p[i]) {
				res++;
			}
		} {
			int[] a = { p[i - 1], p[i], p[i + 1] };
			Arrays.sort(a);
			if (a[1] == p[i]) {
				res++;
			}
		} int[] a = { p[i - 1], p[i], p[i + 1] }; a { p[i - 1], p[i], p[i + 1] } p[i - 1] p i - 1 i 1 p[i] p i p[i + 1] p i + 1 i 1 Arrays.sort(a) Arrays.sort Arrays a if (a[1] == p[i]) {
				res++;
			} a[1] == p[i] a[1] a 1 p[i] p i {
				res++;
			} res++ res System.out.println(res) System.out.println System.out System System.out res String[] args args public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();
		int[] p = new int[n];
		int res = 0;

		for (int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}
		for (int i = 1; i < n - 1; i++) {
			int[] a = { p[i - 1], p[i], p[i + 1] };
			Arrays.sort(a);
			if (a[1] == p[i]) {
				res++;
			}
		}

		System.out.println(res);
	}
} public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();
		int[] p = new int[n];
		int res = 0;

		for (int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}
		for (int i = 1; i < n - 1; i++) {
			int[] a = { p[i - 1], p[i], p[i + 1] };
			Arrays.sort(a);
			if (a[1] == p[i]) {
				res++;
			}
		}

		System.out.println(res);
	}
} Main
import java.util.Arrays;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();
		int[] p = new int[n];
		int res = 0;

		for (int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}
		for (int i = 1; i < n - 1; i++) {
			int[] a = { p[i - 1], p[i], p[i + 1] };
			Arrays.sort(a);
			if (a[1] == p[i]) {
				res++;
			}
		}

		System.out.println(res);
	}
}