import java.util.Scanner;

public class Main {

	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int[] h = new int[N];
		for (int i = 0; i < h.length; i++) {
			h[i] = sc.nextInt();
		}
		sc.close();
		int pre = -1;
		for (int i = 0; i < h.length; i++) {
			if (pre <= h[i] - 1)
				pre = h[i] - 1;
			else if (pre <= h[i]) {
				pre = h[i];
			} else {
				System.out.println("No");
				return;
			}
		}
		System.out.println("Yes");
	}
} import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int[] h = new int[N];
		for (int i = 0; i < h.length; i++) {
			h[i] = sc.nextInt();
		}
		sc.close();
		int pre = -1;
		for (int i = 0; i < h.length; i++) {
			if (pre <= h[i] - 1)
				pre = h[i] - 1;
			else if (pre <= h[i]) {
				pre = h[i];
			} else {
				System.out.println("No");
				return;
			}
		}
		System.out.println("Yes");
	}
} Main public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int[] h = new int[N];
		for (int i = 0; i < h.length; i++) {
			h[i] = sc.nextInt();
		}
		sc.close();
		int pre = -1;
		for (int i = 0; i < h.length; i++) {
			if (pre <= h[i] - 1)
				pre = h[i] - 1;
			else if (pre <= h[i]) {
				pre = h[i];
			} else {
				System.out.println("No");
				return;
			}
		}
		System.out.println("Yes");
	} main {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int[] h = new int[N];
		for (int i = 0; i < h.length; i++) {
			h[i] = sc.nextInt();
		}
		sc.close();
		int pre = -1;
		for (int i = 0; i < h.length; i++) {
			if (pre <= h[i] - 1)
				pre = h[i] - 1;
			else if (pre <= h[i]) {
				pre = h[i];
			} else {
				System.out.println("No");
				return;
			}
		}
		System.out.println("Yes");
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int N = sc.nextInt(); N sc.nextInt() sc.nextInt sc int[] h = new int[N]; h new int[N] N for (int i = 0; i < h.length; i++) {
			h[i] = sc.nextInt();
		} int i = 0; int i = 0; i 0 i < h.length i h.length h h.length i++ i++ i {
			h[i] = sc.nextInt();
		} {
			h[i] = sc.nextInt();
		} h[i] = sc.nextInt() h[i] h i sc.nextInt() sc.nextInt sc sc.close() sc.close sc int pre = -1; pre -1 1 for (int i = 0; i < h.length; i++) {
			if (pre <= h[i] - 1)
				pre = h[i] - 1;
			else if (pre <= h[i]) {
				pre = h[i];
			} else {
				System.out.println("No");
				return;
			}
		} int i = 0; int i = 0; i 0 i < h.length i h.length h h.length i++ i++ i {
			if (pre <= h[i] - 1)
				pre = h[i] - 1;
			else if (pre <= h[i]) {
				pre = h[i];
			} else {
				System.out.println("No");
				return;
			}
		} {
			if (pre <= h[i] - 1)
				pre = h[i] - 1;
			else if (pre <= h[i]) {
				pre = h[i];
			} else {
				System.out.println("No");
				return;
			}
		} if (pre <= h[i] - 1)
				pre = h[i] - 1;
			else if (pre <= h[i]) {
				pre = h[i];
			} else {
				System.out.println("No");
				return;
			} pre <= h[i] - 1 pre h[i] - 1 h[i] h i 1 pre = h[i] - 1 pre h[i] - 1 h[i] h i 1 if (pre <= h[i]) {
				pre = h[i];
			} else {
				System.out.println("No");
				return;
			} pre <= h[i] pre h[i] h i {
				pre = h[i];
			} pre = h[i] pre h[i] h i {
				System.out.println("No");
				return;
			} System.out.println("No") System.out.println System.out System System.out "No" return; System.out.println("Yes") System.out.println System.out System System.out "Yes" String[] args args public class Main {

	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int[] h = new int[N];
		for (int i = 0; i < h.length; i++) {
			h[i] = sc.nextInt();
		}
		sc.close();
		int pre = -1;
		for (int i = 0; i < h.length; i++) {
			if (pre <= h[i] - 1)
				pre = h[i] - 1;
			else if (pre <= h[i]) {
				pre = h[i];
			} else {
				System.out.println("No");
				return;
			}
		}
		System.out.println("Yes");
	}
} public class Main {

	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int[] h = new int[N];
		for (int i = 0; i < h.length; i++) {
			h[i] = sc.nextInt();
		}
		sc.close();
		int pre = -1;
		for (int i = 0; i < h.length; i++) {
			if (pre <= h[i] - 1)
				pre = h[i] - 1;
			else if (pre <= h[i]) {
				pre = h[i];
			} else {
				System.out.println("No");
				return;
			}
		}
		System.out.println("Yes");
	}
} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int[] h = new int[N];
		for (int i = 0; i < h.length; i++) {
			h[i] = sc.nextInt();
		}
		sc.close();
		int pre = -1;
		for (int i = 0; i < h.length; i++) {
			if (pre <= h[i] - 1)
				pre = h[i] - 1;
			else if (pre <= h[i]) {
				pre = h[i];
			} else {
				System.out.println("No");
				return;
			}
		}
		System.out.println("Yes");
	}
}