
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];
		for(int i = 0 ; i < n ; i++) {
			p[i] = sc.nextInt();
		}
		int ans = 0;
		for(int i = 0 ; i < n ; i++) {
			if(i >= 1 && i < n - 1) {
				if(p[i - 1] < p[i] && p[i] < p[i + 1]) {
					ans++;
				} else if(p[i - 1] > p[i] && p[i] > p[i + 1]) {
					ans++;
				}
			}
		}
		System.out.println(ans);
		sc.close();

	}

} 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];
		for(int i = 0 ; i < n ; i++) {
			p[i] = sc.nextInt();
		}
		int ans = 0;
		for(int i = 0 ; i < n ; i++) {
			if(i >= 1 && i < n - 1) {
				if(p[i - 1] < p[i] && p[i] < p[i + 1]) {
					ans++;
				} else if(p[i - 1] > p[i] && p[i] > p[i + 1]) {
					ans++;
				}
			}
		}
		System.out.println(ans);
		sc.close();

	}

} Main public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] p = new int[n];
		for(int i = 0 ; i < n ; i++) {
			p[i] = sc.nextInt();
		}
		int ans = 0;
		for(int i = 0 ; i < n ; i++) {
			if(i >= 1 && i < n - 1) {
				if(p[i - 1] < p[i] && p[i] < p[i + 1]) {
					ans++;
				} else if(p[i - 1] > p[i] && p[i] > p[i + 1]) {
					ans++;
				}
			}
		}
		System.out.println(ans);
		sc.close();

	} main {

		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] p = new int[n];
		for(int i = 0 ; i < n ; i++) {
			p[i] = sc.nextInt();
		}
		int ans = 0;
		for(int i = 0 ; i < n ; i++) {
			if(i >= 1 && i < n - 1) {
				if(p[i - 1] < p[i] && p[i] < p[i + 1]) {
					ans++;
				} else if(p[i - 1] > p[i] && p[i] > p[i + 1]) {
					ans++;
				}
			}
		}
		System.out.println(ans);
		sc.close();

	} 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 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 ans = 0; ans 0 for(int i = 0 ; i < n ; i++) {
			if(i >= 1 && i < n - 1) {
				if(p[i - 1] < p[i] && p[i] < p[i + 1]) {
					ans++;
				} else if(p[i - 1] > p[i] && p[i] > p[i + 1]) {
					ans++;
				}
			}
		} int i = 0 ; int i = 0 ; i 0 i < n i n i++ i++ i {
			if(i >= 1 && i < n - 1) {
				if(p[i - 1] < p[i] && p[i] < p[i + 1]) {
					ans++;
				} else if(p[i - 1] > p[i] && p[i] > p[i + 1]) {
					ans++;
				}
			}
		} {
			if(i >= 1 && i < n - 1) {
				if(p[i - 1] < p[i] && p[i] < p[i + 1]) {
					ans++;
				} else if(p[i - 1] > p[i] && p[i] > p[i + 1]) {
					ans++;
				}
			}
		} if(i >= 1 && i < n - 1) {
				if(p[i - 1] < p[i] && p[i] < p[i + 1]) {
					ans++;
				} else if(p[i - 1] > p[i] && p[i] > p[i + 1]) {
					ans++;
				}
			} i >= 1 && i < n - 1 i >= 1 i 1 i < n - 1 i n - 1 n 1 {
				if(p[i - 1] < p[i] && p[i] < p[i + 1]) {
					ans++;
				} else if(p[i - 1] > p[i] && p[i] > p[i + 1]) {
					ans++;
				}
			} if(p[i - 1] < p[i] && p[i] < p[i + 1]) {
					ans++;
				} else if(p[i - 1] > p[i] && p[i] > p[i + 1]) {
					ans++;
				} 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 {
					ans++;
				} ans++ ans if(p[i - 1] > p[i] && p[i] > p[i + 1]) {
					ans++;
				} 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 {
					ans++;
				} ans++ ans System.out.println(ans) System.out.println System.out System System.out ans sc.close() sc.close sc 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];
		for(int i = 0 ; i < n ; i++) {
			p[i] = sc.nextInt();
		}
		int ans = 0;
		for(int i = 0 ; i < n ; i++) {
			if(i >= 1 && i < n - 1) {
				if(p[i - 1] < p[i] && p[i] < p[i + 1]) {
					ans++;
				} else if(p[i - 1] > p[i] && p[i] > p[i + 1]) {
					ans++;
				}
			}
		}
		System.out.println(ans);
		sc.close();

	}

} public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] p = new int[n];
		for(int i = 0 ; i < n ; i++) {
			p[i] = sc.nextInt();
		}
		int ans = 0;
		for(int i = 0 ; i < n ; i++) {
			if(i >= 1 && i < n - 1) {
				if(p[i - 1] < p[i] && p[i] < p[i + 1]) {
					ans++;
				} else if(p[i - 1] > p[i] && p[i] > p[i + 1]) {
					ans++;
				}
			}
		}
		System.out.println(ans);
		sc.close();

	}

} Main

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];
		for(int i = 0 ; i < n ; i++) {
			p[i] = sc.nextInt();
		}
		int ans = 0;
		for(int i = 0 ; i < n ; i++) {
			if(i >= 1 && i < n - 1) {
				if(p[i - 1] < p[i] && p[i] < p[i + 1]) {
					ans++;
				} else if(p[i - 1] > p[i] && p[i] > p[i + 1]) {
					ans++;
				}
			}
		}
		System.out.println(ans);
		sc.close();

	}

}
