
import java.util.Scanner;

public class Main {
	public static void main(String arg[]) {

		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();

		int count = 0;

		int p[] = new int[n];

		for (int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}

		for (int i = 1; i < n - 1; i++) {
			if (p[i - 1] < p[i] && p[i] < p[i + 1]) {
				count++;
			} else if (p[i - 1] > p[i] && p[i] > p[i + 1]) {
				count++;
			}
		}
		System.out.print(count);
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String arg[]) {

		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();

		int count = 0;

		int p[] = new int[n];

		for (int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}

		for (int i = 1; i < n - 1; i++) {
			if (p[i - 1] < p[i] && p[i] < p[i + 1]) {
				count++;
			} else if (p[i - 1] > p[i] && p[i] > p[i + 1]) {
				count++;
			}
		}
		System.out.print(count);
	}
} Main public static void main(String arg[]) {

		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();

		int count = 0;

		int p[] = new int[n];

		for (int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}

		for (int i = 1; i < n - 1; i++) {
			if (p[i - 1] < p[i] && p[i] < p[i + 1]) {
				count++;
			} else if (p[i - 1] > p[i] && p[i] > p[i + 1]) {
				count++;
			}
		}
		System.out.print(count);
	} main {

		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();

		int count = 0;

		int p[] = new int[n];

		for (int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}

		for (int i = 1; i < n - 1; i++) {
			if (p[i - 1] < p[i] && p[i] < p[i + 1]) {
				count++;
			} else if (p[i - 1] > p[i] && p[i] > p[i + 1]) {
				count++;
			}
		}
		System.out.print(count);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int count = 0; count 0 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 for (int i = 1; i < n - 1; i++) {
			if (p[i - 1] < p[i] && p[i] < p[i + 1]) {
				count++;
			} else if (p[i - 1] > p[i] && p[i] > p[i + 1]) {
				count++;
			}
		} 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]) {
				count++;
			} else if (p[i - 1] > p[i] && p[i] > p[i + 1]) {
				count++;
			}
		} {
			if (p[i - 1] < p[i] && p[i] < p[i + 1]) {
				count++;
			} else if (p[i - 1] > p[i] && p[i] > p[i + 1]) {
				count++;
			}
		} if (p[i - 1] < p[i] && p[i] < p[i + 1]) {
				count++;
			} else if (p[i - 1] > p[i] && p[i] > p[i + 1]) {
				count++;
			} 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 {
				count++;
			} count++ count if (p[i - 1] > p[i] && p[i] > p[i + 1]) {
				count++;
			} 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 {
				count++;
			} count++ count System.out.print(count) System.out.print System.out System System.out count String arg[] arg public class Main {
	public static void main(String arg[]) {

		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();

		int count = 0;

		int p[] = new int[n];

		for (int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}

		for (int i = 1; i < n - 1; i++) {
			if (p[i - 1] < p[i] && p[i] < p[i + 1]) {
				count++;
			} else if (p[i - 1] > p[i] && p[i] > p[i + 1]) {
				count++;
			}
		}
		System.out.print(count);
	}
} public class Main {
	public static void main(String arg[]) {

		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();

		int count = 0;

		int p[] = new int[n];

		for (int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}

		for (int i = 1; i < n - 1; i++) {
			if (p[i - 1] < p[i] && p[i] < p[i + 1]) {
				count++;
			} else if (p[i - 1] > p[i] && p[i] > p[i + 1]) {
				count++;
			}
		}
		System.out.print(count);
	}
} Main

import java.util.Scanner;

public class Main {
	public static void main(String arg[]) {

		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();

		int count = 0;

		int p[] = new int[n];

		for (int i = 0; i < n; i++) {
			p[i] = sc.nextInt();
		}

		for (int i = 1; i < n - 1; i++) {
			if (p[i - 1] < p[i] && p[i] < p[i + 1]) {
				count++;
			} else if (p[i - 1] > p[i] && p[i] > p[i + 1]) {
				count++;
			}
		}
		System.out.print(count);
	}
}
