import 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 count = 0;
        for(int i = 0; i < N-2; ++i){
            if(P[i] < P[i+1] && P[i+1] < P[i+2] || P[i] > P[i+1] && P[i+1] > P[i+2]){
             count += 1;   
            }
        }
        System.out.println(count);
	}
} import java.util.*; util.* java 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 count = 0;
        for(int i = 0; i < N-2; ++i){
            if(P[i] < P[i+1] && P[i+1] < P[i+2] || P[i] > P[i+1] && P[i+1] > P[i+2]){
             count += 1;   
            }
        }
        System.out.println(count);
	}
} 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 count = 0;
        for(int i = 0; i < N-2; ++i){
            if(P[i] < P[i+1] && P[i+1] < P[i+2] || P[i] > P[i+1] && P[i+1] > P[i+2]){
             count += 1;   
            }
        }
        System.out.println(count);
	} 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 count = 0;
        for(int i = 0; i < N-2; ++i){
            if(P[i] < P[i+1] && P[i+1] < P[i+2] || P[i] > P[i+1] && P[i+1] > P[i+2]){
             count += 1;   
            }
        }
        System.out.println(count);
	} 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 count = 0; count 0 for(int i = 0; i < N-2; ++i){
            if(P[i] < P[i+1] && P[i+1] < P[i+2] || P[i] > P[i+1] && P[i+1] > P[i+2]){
             count += 1;   
            }
        } int i = 0; int i = 0; i 0 i < N-2 i N-2 N 2 ++i ++i i {
            if(P[i] < P[i+1] && P[i+1] < P[i+2] || P[i] > P[i+1] && P[i+1] > P[i+2]){
             count += 1;   
            }
        } {
            if(P[i] < P[i+1] && P[i+1] < P[i+2] || P[i] > P[i+1] && P[i+1] > P[i+2]){
             count += 1;   
            }
        } if(P[i] < P[i+1] && P[i+1] < P[i+2] || P[i] > P[i+1] && P[i+1] > P[i+2]){
             count += 1;   
            } P[i] < P[i+1] && P[i+1] < P[i+2] || P[i] > P[i+1] && P[i+1] > P[i+2] P[i] < P[i+1] && P[i+1] < P[i+2] P[i] < P[i+1] P[i] P i P[i+1] P i+1 i 1 P[i+1] < P[i+2] P[i+1] P i+1 i 1 P[i+2] P i+2 i 2 P[i] > P[i+1] && P[i+1] > P[i+2] P[i] > P[i+1] P[i] P i P[i+1] P i+1 i 1 P[i+1] > P[i+2] P[i+1] P i+1 i 1 P[i+2] P i+2 i 2 {
             count += 1;   
            } count += 1 count 1 System.out.println(count) System.out.println System.out System System.out count 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 count = 0;
        for(int i = 0; i < N-2; ++i){
            if(P[i] < P[i+1] && P[i+1] < P[i+2] || P[i] > P[i+1] && P[i+1] > P[i+2]){
             count += 1;   
            }
        }
        System.out.println(count);
	}
} 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 count = 0;
        for(int i = 0; i < N-2; ++i){
            if(P[i] < P[i+1] && P[i+1] < P[i+2] || P[i] > P[i+1] && P[i+1] > P[i+2]){
             count += 1;   
            }
        }
        System.out.println(count);
	}
} Main
import 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 count = 0;
        for(int i = 0; i < N-2; ++i){
            if(P[i] < P[i+1] && P[i+1] < P[i+2] || P[i] > P[i+1] && P[i+1] > P[i+2]){
             count += 1;   
            }
        }
        System.out.println(count);
	}
}