import java.util.*;

import static java.lang.Integer.*;
//import static java.lang.Long.*;
//import static java.lang.Math.*;

public class Main {
	public static void main(String[] args) {
		int i,j;
		Scanner sc = new Scanner(System.in);
		int n = parseInt(sc.next());
		int[] p = new int[n];
		for(i=0;i<n;i++) {
			p[i] = parseInt(sc.next());
		}
		sc.close();
		int cnt=0;
		for(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.*; util.* java import static java.lang.Integer.*; import static java.lang.Integer.*; import static java.lang.Integer.*; public class Main {
	public static void main(String[] args) {
		int i,j;
		Scanner sc = new Scanner(System.in);
		int n = parseInt(sc.next());
		int[] p = new int[n];
		for(i=0;i<n;i++) {
			p[i] = parseInt(sc.next());
		}
		sc.close();
		int cnt=0;
		for(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) {
		int i,j;
		Scanner sc = new Scanner(System.in);
		int n = parseInt(sc.next());
		int[] p = new int[n];
		for(i=0;i<n;i++) {
			p[i] = parseInt(sc.next());
		}
		sc.close();
		int cnt=0;
		for(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 {
		int i,j;
		Scanner sc = new Scanner(System.in);
		int n = parseInt(sc.next());
		int[] p = new int[n];
		for(i=0;i<n;i++) {
			p[i] = parseInt(sc.next());
		}
		sc.close();
		int cnt=0;
		for(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);
	} int i i j; j Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = parseInt(sc.next()); n parseInt(sc.next()) parseInt sc.next() sc.next sc int[] p = new int[n]; p new int[n] n for(i=0;i<n;i++) {
			p[i] = parseInt(sc.next());
		} i=0; i=0 i 0 i<n i n i++ i++ i {
			p[i] = parseInt(sc.next());
		} {
			p[i] = parseInt(sc.next());
		} p[i] = parseInt(sc.next()) p[i] p i parseInt(sc.next()) parseInt sc.next() sc.next sc sc.close() sc.close sc int cnt=0; cnt 0 for(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++;
			}
		} i=1; 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) {
		int i,j;
		Scanner sc = new Scanner(System.in);
		int n = parseInt(sc.next());
		int[] p = new int[n];
		for(i=0;i<n;i++) {
			p[i] = parseInt(sc.next());
		}
		sc.close();
		int cnt=0;
		for(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) {
		int i,j;
		Scanner sc = new Scanner(System.in);
		int n = parseInt(sc.next());
		int[] p = new int[n];
		for(i=0;i<n;i++) {
			p[i] = parseInt(sc.next());
		}
		sc.close();
		int cnt=0;
		for(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.*;

import static java.lang.Integer.*;
//import static java.lang.Long.*;
//import static java.lang.Math.*;

public class Main {
	public static void main(String[] args) {
		int i,j;
		Scanner sc = new Scanner(System.in);
		int n = parseInt(sc.next());
		int[] p = new int[n];
		for(i=0;i<n;i++) {
			p[i] = parseInt(sc.next());
		}
		sc.close();
		int cnt=0;
		for(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);
	}
}
