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 < n; i++) {
			h[i] = sc.nextInt();
		}
		sc.close();

		h[0]--;
		for (int i = 1; i < n; i++) {
			if (h[i] < h[i - 1]) {
				System.out.println("No");
				return;
			}
			if (h[i] > h[i - 1]) {
				h[i]--;
			}
		}
		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 < n; i++) {
			h[i] = sc.nextInt();
		}
		sc.close();

		h[0]--;
		for (int i = 1; i < n; i++) {
			if (h[i] < h[i - 1]) {
				System.out.println("No");
				return;
			}
			if (h[i] > h[i - 1]) {
				h[i]--;
			}
		}
		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 < n; i++) {
			h[i] = sc.nextInt();
		}
		sc.close();

		h[0]--;
		for (int i = 1; i < n; i++) {
			if (h[i] < h[i - 1]) {
				System.out.println("No");
				return;
			}
			if (h[i] > h[i - 1]) {
				h[i]--;
			}
		}
		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 < n; i++) {
			h[i] = sc.nextInt();
		}
		sc.close();

		h[0]--;
		for (int i = 1; i < n; i++) {
			if (h[i] < h[i - 1]) {
				System.out.println("No");
				return;
			}
			if (h[i] > h[i - 1]) {
				h[i]--;
			}
		}
		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 < n; i++) {
			h[i] = sc.nextInt();
		} int i = 0; int i = 0; i 0 i < n i n 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 h[0]-- h[0] h 0 for (int i = 1; i < n; i++) {
			if (h[i] < h[i - 1]) {
				System.out.println("No");
				return;
			}
			if (h[i] > h[i - 1]) {
				h[i]--;
			}
		} int i = 1; int i = 1; i 1 i < n i n i++ i++ i {
			if (h[i] < h[i - 1]) {
				System.out.println("No");
				return;
			}
			if (h[i] > h[i - 1]) {
				h[i]--;
			}
		} {
			if (h[i] < h[i - 1]) {
				System.out.println("No");
				return;
			}
			if (h[i] > h[i - 1]) {
				h[i]--;
			}
		} if (h[i] < h[i - 1]) {
				System.out.println("No");
				return;
			} h[i] < h[i - 1] h[i] h i h[i - 1] h i - 1 i 1 {
				System.out.println("No");
				return;
			} System.out.println("No") System.out.println System.out System System.out "No" return; if (h[i] > h[i - 1]) {
				h[i]--;
			} h[i] > h[i - 1] h[i] h i h[i - 1] h i - 1 i 1 {
				h[i]--;
			} h[i]-- h[i] h i 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 < n; i++) {
			h[i] = sc.nextInt();
		}
		sc.close();

		h[0]--;
		for (int i = 1; i < n; i++) {
			if (h[i] < h[i - 1]) {
				System.out.println("No");
				return;
			}
			if (h[i] > h[i - 1]) {
				h[i]--;
			}
		}
		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 < n; i++) {
			h[i] = sc.nextInt();
		}
		sc.close();

		h[0]--;
		for (int i = 1; i < n; i++) {
			if (h[i] < h[i - 1]) {
				System.out.println("No");
				return;
			}
			if (h[i] > h[i - 1]) {
				h[i]--;
			}
		}
		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 < n; i++) {
			h[i] = sc.nextInt();
		}
		sc.close();

		h[0]--;
		for (int i = 1; i < n; i++) {
			if (h[i] < h[i - 1]) {
				System.out.println("No");
				return;
			}
			if (h[i] > h[i - 1]) {
				h[i]--;
			}
		}
		System.out.println("Yes");
	}
}
