import java.util.Scanner;
public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);

		int n = in.nextInt();
		int[] p = new int[n];
		int cnt = 0;
		for ( int i = 0; i < n; i++ ) {
			p[i] = in.nextInt();
		}

		for ( int i = 0; i < n; i++ ) {

			if ( 1 <= i && i <= n - 2 ) {
				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);
		in.close();
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);

		int n = in.nextInt();
		int[] p = new int[n];
		int cnt = 0;
		for ( int i = 0; i < n; i++ ) {
			p[i] = in.nextInt();
		}

		for ( int i = 0; i < n; i++ ) {

			if ( 1 <= i && i <= n - 2 ) {
				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);
		in.close();
	}
} Main public static void main(String[] args) {
		Scanner in = new Scanner(System.in);

		int n = in.nextInt();
		int[] p = new int[n];
		int cnt = 0;
		for ( int i = 0; i < n; i++ ) {
			p[i] = in.nextInt();
		}

		for ( int i = 0; i < n; i++ ) {

			if ( 1 <= i && i <= n - 2 ) {
				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);
		in.close();
	} main {
		Scanner in = new Scanner(System.in);

		int n = in.nextInt();
		int[] p = new int[n];
		int cnt = 0;
		for ( int i = 0; i < n; i++ ) {
			p[i] = in.nextInt();
		}

		for ( int i = 0; i < n; i++ ) {

			if ( 1 <= i && i <= n - 2 ) {
				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);
		in.close();
	} Scanner in = new Scanner(System.in); in new Scanner(System.in) int n = in.nextInt(); n in.nextInt() in.nextInt in int[] p = new int[n]; p new int[n] n int cnt = 0; cnt 0 for ( int i = 0; i < n; i++ ) {
			p[i] = in.nextInt();
		} int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
			p[i] = in.nextInt();
		} {
			p[i] = in.nextInt();
		} p[i] = in.nextInt() p[i] p i in.nextInt() in.nextInt in for ( int i = 0; i < n; i++ ) {

			if ( 1 <= i && i <= n - 2 ) {
				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 = 0; int i = 0; i 0 i < n i n i++ i++ i {

			if ( 1 <= i && i <= n - 2 ) {
				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 ( 1 <= i && i <= n - 2 ) {
				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 ( 1 <= i && i <= n - 2 ) {
				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++;
				}
			} 1 <= i && i <= n - 2 1 <= i 1 i i <= n - 2 i n - 2 n 2 {
				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 in.close() in.close in String[] args args public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);

		int n = in.nextInt();
		int[] p = new int[n];
		int cnt = 0;
		for ( int i = 0; i < n; i++ ) {
			p[i] = in.nextInt();
		}

		for ( int i = 0; i < n; i++ ) {

			if ( 1 <= i && i <= n - 2 ) {
				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);
		in.close();
	}
} public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);

		int n = in.nextInt();
		int[] p = new int[n];
		int cnt = 0;
		for ( int i = 0; i < n; i++ ) {
			p[i] = in.nextInt();
		}

		for ( int i = 0; i < n; i++ ) {

			if ( 1 <= i && i <= n - 2 ) {
				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);
		in.close();
	}
} Main
import java.util.Scanner;
public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);

		int n = in.nextInt();
		int[] p = new int[n];
		int cnt = 0;
		for ( int i = 0; i < n; i++ ) {
			p[i] = in.nextInt();
		}

		for ( int i = 0; i < n; i++ ) {

			if ( 1 <= i && i <= n - 2 ) {
				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);
		in.close();
	}
}