import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        Integer[] p = new Integer[n];
        for (int i = 0; i < n; i++) {
            p[i] = sc.nextInt();
        }
        sc.close();

        int count = 0;
        for (int i = 1; i < n - 1; i++) {
            if (p[i - 1] == p[i + 1]) {
                if (p[i] < p[i + 1]) {
                    count++;
                }
            } else if (p[i - 1] < p[i + 1]) {
                if (p[i - 1] <= p[i] && p[i] < p[i + 1]) {
                    count++;
                }
            } else if (p[i - 1] > p[i + 1]) {
                if (p[i - 1] > p[i] && p[i] >= p[i + 1]) {
                    count++;
                }
            }
        }

        System.out.println(count);
    }
} 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();
        Integer[] p = new Integer[n];
        for (int i = 0; i < n; i++) {
            p[i] = sc.nextInt();
        }
        sc.close();

        int count = 0;
        for (int i = 1; i < n - 1; i++) {
            if (p[i - 1] == p[i + 1]) {
                if (p[i] < p[i + 1]) {
                    count++;
                }
            } else if (p[i - 1] < p[i + 1]) {
                if (p[i - 1] <= p[i] && p[i] < p[i + 1]) {
                    count++;
                }
            } else if (p[i - 1] > p[i + 1]) {
                if (p[i - 1] > p[i] && p[i] >= p[i + 1]) {
                    count++;
                }
            }
        }

        System.out.println(count);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        Integer[] p = new Integer[n];
        for (int i = 0; i < n; i++) {
            p[i] = sc.nextInt();
        }
        sc.close();

        int count = 0;
        for (int i = 1; i < n - 1; i++) {
            if (p[i - 1] == p[i + 1]) {
                if (p[i] < p[i + 1]) {
                    count++;
                }
            } else if (p[i - 1] < p[i + 1]) {
                if (p[i - 1] <= p[i] && p[i] < p[i + 1]) {
                    count++;
                }
            } else if (p[i - 1] > p[i + 1]) {
                if (p[i - 1] > p[i] && p[i] >= p[i + 1]) {
                    count++;
                }
            }
        }

        System.out.println(count);
    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        Integer[] p = new Integer[n];
        for (int i = 0; i < n; i++) {
            p[i] = sc.nextInt();
        }
        sc.close();

        int count = 0;
        for (int i = 1; i < n - 1; i++) {
            if (p[i - 1] == p[i + 1]) {
                if (p[i] < p[i + 1]) {
                    count++;
                }
            } else if (p[i - 1] < p[i + 1]) {
                if (p[i - 1] <= p[i] && p[i] < p[i + 1]) {
                    count++;
                }
            } else if (p[i - 1] > p[i + 1]) {
                if (p[i - 1] > p[i] && p[i] >= p[i + 1]) {
                    count++;
                }
            }
        }

        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 Integer[] p = new Integer[n]; p new Integer[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 sc.close() sc.close sc int count = 0; count 0 for (int i = 1; i < n - 1; i++) {
            if (p[i - 1] == p[i + 1]) {
                if (p[i] < p[i + 1]) {
                    count++;
                }
            } else if (p[i - 1] < p[i + 1]) {
                if (p[i - 1] <= p[i] && p[i] < p[i + 1]) {
                    count++;
                }
            } else if (p[i - 1] > p[i + 1]) {
                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 + 1]) {
                if (p[i] < p[i + 1]) {
                    count++;
                }
            } else if (p[i - 1] < p[i + 1]) {
                if (p[i - 1] <= p[i] && p[i] < p[i + 1]) {
                    count++;
                }
            } else if (p[i - 1] > p[i + 1]) {
                if (p[i - 1] > p[i] && p[i] >= p[i + 1]) {
                    count++;
                }
            }
        } {
            if (p[i - 1] == p[i + 1]) {
                if (p[i] < p[i + 1]) {
                    count++;
                }
            } else if (p[i - 1] < p[i + 1]) {
                if (p[i - 1] <= p[i] && p[i] < p[i + 1]) {
                    count++;
                }
            } else if (p[i - 1] > p[i + 1]) {
                if (p[i - 1] > p[i] && p[i] >= p[i + 1]) {
                    count++;
                }
            }
        } if (p[i - 1] == p[i + 1]) {
                if (p[i] < p[i + 1]) {
                    count++;
                }
            } else if (p[i - 1] < p[i + 1]) {
                if (p[i - 1] <= p[i] && p[i] < p[i + 1]) {
                    count++;
                }
            } else if (p[i - 1] > p[i + 1]) {
                if (p[i - 1] > p[i] && p[i] >= p[i + 1]) {
                    count++;
                }
            } p[i - 1] == p[i + 1] p[i - 1] p i - 1 i 1 p[i + 1] p i + 1 i 1 {
                if (p[i] < p[i + 1]) {
                    count++;
                }
            } if (p[i] < p[i + 1]) {
                    count++;
                } 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 + 1]) {
                if (p[i - 1] <= p[i] && p[i] < p[i + 1]) {
                    count++;
                }
            } else if (p[i - 1] > p[i + 1]) {
                if (p[i - 1] > p[i] && p[i] >= p[i + 1]) {
                    count++;
                }
            } p[i - 1] < p[i + 1] p[i - 1] p i - 1 i 1 p[i + 1] p i + 1 i 1 {
                if (p[i - 1] <= p[i] && p[i] < p[i + 1]) {
                    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 if (p[i - 1] > p[i + 1]) {
                if (p[i - 1] > p[i] && p[i] >= p[i + 1]) {
                    count++;
                }
            } p[i - 1] > p[i + 1] p[i - 1] p i - 1 i 1 p[i + 1] p i + 1 i 1 {
                if (p[i - 1] > p[i] && p[i] >= p[i + 1]) {
                    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.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();
        Integer[] p = new Integer[n];
        for (int i = 0; i < n; i++) {
            p[i] = sc.nextInt();
        }
        sc.close();

        int count = 0;
        for (int i = 1; i < n - 1; i++) {
            if (p[i - 1] == p[i + 1]) {
                if (p[i] < p[i + 1]) {
                    count++;
                }
            } else if (p[i - 1] < p[i + 1]) {
                if (p[i - 1] <= p[i] && p[i] < p[i + 1]) {
                    count++;
                }
            } else if (p[i - 1] > p[i + 1]) {
                if (p[i - 1] > p[i] && p[i] >= p[i + 1]) {
                    count++;
                }
            }
        }

        System.out.println(count);
    }
} public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        Integer[] p = new Integer[n];
        for (int i = 0; i < n; i++) {
            p[i] = sc.nextInt();
        }
        sc.close();

        int count = 0;
        for (int i = 1; i < n - 1; i++) {
            if (p[i - 1] == p[i + 1]) {
                if (p[i] < p[i + 1]) {
                    count++;
                }
            } else if (p[i - 1] < p[i + 1]) {
                if (p[i - 1] <= p[i] && p[i] < p[i + 1]) {
                    count++;
                }
            } else if (p[i - 1] > p[i + 1]) {
                if (p[i - 1] > p[i] && p[i] >= p[i + 1]) {
                    count++;
                }
            }
        }

        System.out.println(count);
    }
} Main
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        Integer[] p = new Integer[n];
        for (int i = 0; i < n; i++) {
            p[i] = sc.nextInt();
        }
        sc.close();

        int count = 0;
        for (int i = 1; i < n - 1; i++) {
            if (p[i - 1] == p[i + 1]) {
                if (p[i] < p[i + 1]) {
                    count++;
                }
            } else if (p[i - 1] < p[i + 1]) {
                if (p[i - 1] <= p[i] && p[i] < p[i + 1]) {
                    count++;
                }
            } else if (p[i - 1] > p[i + 1]) {
                if (p[i - 1] > p[i] && p[i] >= p[i + 1]) {
                    count++;
                }
            }
        }

        System.out.println(count);
    }
}