import java.util.*;

public class Main{
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        Integer N = sc.nextInt();
        int p[] = new int[N+1];
        for(int i=1; i<=N; i++) {
            p[i] = sc.nextInt();
        }
        int cnt=0;
        for(int i=2; i<=N-1; i++) {
            if(p[i-1] < p[i] && p[i] < p[i+1]) {
                cnt++;
            } else if(p[i-1] > p[i] && p[i] > p[i+1]) {
                cnt++;
            }
        }
        System.out.println(cnt);
    }
} import java.util.*; util.* java public class Main{
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        Integer N = sc.nextInt();
        int p[] = new int[N+1];
        for(int i=1; i<=N; i++) {
            p[i] = sc.nextInt();
        }
        int cnt=0;
        for(int i=2; i<=N-1; i++) {
            if(p[i-1] < p[i] && p[i] < p[i+1]) {
                cnt++;
            } else if(p[i-1] > p[i] && p[i] > p[i+1]) {
                cnt++;
            }
        }
        System.out.println(cnt);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        Integer N = sc.nextInt();
        int p[] = new int[N+1];
        for(int i=1; i<=N; i++) {
            p[i] = sc.nextInt();
        }
        int cnt=0;
        for(int i=2; i<=N-1; i++) {
            if(p[i-1] < p[i] && p[i] < p[i+1]) {
                cnt++;
            } else if(p[i-1] > p[i] && p[i] > p[i+1]) {
                cnt++;
            }
        }
        System.out.println(cnt);
    } main {
        Scanner sc = new Scanner(System.in);
        Integer N = sc.nextInt();
        int p[] = new int[N+1];
        for(int i=1; i<=N; i++) {
            p[i] = sc.nextInt();
        }
        int cnt=0;
        for(int i=2; i<=N-1; i++) {
            if(p[i-1] < p[i] && p[i] < p[i+1]) {
                cnt++;
            } else if(p[i-1] > p[i] && p[i] > p[i+1]) {
                cnt++;
            }
        }
        System.out.println(cnt);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) Integer N = sc.nextInt(); N sc.nextInt() sc.nextInt sc int p[] = new int[N+1]; p new int[N+1] N+1 N 1 for(int i=1; i<=N; i++) {
            p[i] = sc.nextInt();
        } int i=1; int i=1; i 1 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 cnt=0; cnt 0 for(int i=2; i<=N-1; i++) {
            if(p[i-1] < p[i] && p[i] < p[i+1]) {
                cnt++;
            } else if(p[i-1] > p[i] && p[i] > p[i+1]) {
                cnt++;
            }
        } int i=2; int i=2; i 2 i<=N-1 i N-1 N 1 i++ i++ i {
            if(p[i-1] < p[i] && p[i] < p[i+1]) {
                cnt++;
            } else if(p[i-1] > p[i] && p[i] > p[i+1]) {
                cnt++;
            }
        } {
            if(p[i-1] < p[i] && p[i] < p[i+1]) {
                cnt++;
            } else if(p[i-1] > p[i] && p[i] > p[i+1]) {
                cnt++;
            }
        } if(p[i-1] < p[i] && p[i] < p[i+1]) {
                cnt++;
            } else if(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-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 if(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-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) {
        Scanner sc = new Scanner(System.in);
        Integer N = sc.nextInt();
        int p[] = new int[N+1];
        for(int i=1; i<=N; i++) {
            p[i] = sc.nextInt();
        }
        int cnt=0;
        for(int i=2; i<=N-1; i++) {
            if(p[i-1] < p[i] && p[i] < p[i+1]) {
                cnt++;
            } else if(p[i-1] > p[i] && p[i] > p[i+1]) {
                cnt++;
            }
        }
        System.out.println(cnt);
    }
} public class Main{
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        Integer N = sc.nextInt();
        int p[] = new int[N+1];
        for(int i=1; i<=N; i++) {
            p[i] = sc.nextInt();
        }
        int cnt=0;
        for(int i=2; i<=N-1; i++) {
            if(p[i-1] < p[i] && p[i] < p[i+1]) {
                cnt++;
            } else if(p[i-1] > p[i] && p[i] > p[i+1]) {
                cnt++;
            }
        }
        System.out.println(cnt);
    }
} Main
import java.util.*;

public class Main{
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        Integer N = sc.nextInt();
        int p[] = new int[N+1];
        for(int i=1; i<=N; i++) {
            p[i] = sc.nextInt();
        }
        int cnt=0;
        for(int i=2; i<=N-1; i++) {
            if(p[i-1] < p[i] && p[i] < p[i+1]) {
                cnt++;
            } else if(p[i-1] > p[i] && p[i] > p[i+1]) {
                cnt++;
            }
        }
        System.out.println(cnt);
    }
}