import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] h = new int[n];
		boolean flag = true;

		for(int i = 0; i < n; i++) h[i] = sc.nextInt();

		h[0]--;
		for(int i = 1; i < n; i++) {
			if(h[i-1] < h[i]) {
				h[i]--;
			}else if(h[i-1] > h[i]) {
				flag = false;
				break;
			}
		}

		System.out.print(flag ? "Yes" : "No");
		sc.close();
	}
} 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();
		int[] h = new int[n];
		boolean flag = true;

		for(int i = 0; i < n; i++) h[i] = sc.nextInt();

		h[0]--;
		for(int i = 1; i < n; i++) {
			if(h[i-1] < h[i]) {
				h[i]--;
			}else if(h[i-1] > h[i]) {
				flag = false;
				break;
			}
		}

		System.out.print(flag ? "Yes" : "No");
		sc.close();
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] h = new int[n];
		boolean flag = true;

		for(int i = 0; i < n; i++) h[i] = sc.nextInt();

		h[0]--;
		for(int i = 1; i < n; i++) {
			if(h[i-1] < h[i]) {
				h[i]--;
			}else if(h[i-1] > h[i]) {
				flag = false;
				break;
			}
		}

		System.out.print(flag ? "Yes" : "No");
		sc.close();
	} main {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] h = new int[n];
		boolean flag = true;

		for(int i = 0; i < n; i++) h[i] = sc.nextInt();

		h[0]--;
		for(int i = 1; i < n; i++) {
			if(h[i-1] < h[i]) {
				h[i]--;
			}else if(h[i-1] > h[i]) {
				flag = false;
				break;
			}
		}

		System.out.print(flag ? "Yes" : "No");
		sc.close();
	} 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 boolean flag = true; flag true 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] h i sc.nextInt() sc.nextInt sc h[0]-- h[0] h 0 for(int i = 1; i < n; i++) {
			if(h[i-1] < h[i]) {
				h[i]--;
			}else if(h[i-1] > h[i]) {
				flag = false;
				break;
			}
		} int i = 1; int i = 1; i 1 i < n i n i++ i++ i {
			if(h[i-1] < h[i]) {
				h[i]--;
			}else if(h[i-1] > h[i]) {
				flag = false;
				break;
			}
		} {
			if(h[i-1] < h[i]) {
				h[i]--;
			}else if(h[i-1] > h[i]) {
				flag = false;
				break;
			}
		} if(h[i-1] < h[i]) {
				h[i]--;
			}else if(h[i-1] > h[i]) {
				flag = false;
				break;
			} h[i-1] < h[i] h[i-1] h i-1 i 1 h[i] h i {
				h[i]--;
			} h[i]-- h[i] h i if(h[i-1] > h[i]) {
				flag = false;
				break;
			} h[i-1] > h[i] h[i-1] h i-1 i 1 h[i] h i {
				flag = false;
				break;
			} flag = false flag false break; System.out.print(flag ? "Yes" : "No") System.out.print System.out System System.out flag ? "Yes" : "No" flag "Yes" "No" sc.close() sc.close sc String[] args args public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] h = new int[n];
		boolean flag = true;

		for(int i = 0; i < n; i++) h[i] = sc.nextInt();

		h[0]--;
		for(int i = 1; i < n; i++) {
			if(h[i-1] < h[i]) {
				h[i]--;
			}else if(h[i-1] > h[i]) {
				flag = false;
				break;
			}
		}

		System.out.print(flag ? "Yes" : "No");
		sc.close();
	}
} public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] h = new int[n];
		boolean flag = true;

		for(int i = 0; i < n; i++) h[i] = sc.nextInt();

		h[0]--;
		for(int i = 1; i < n; i++) {
			if(h[i-1] < h[i]) {
				h[i]--;
			}else if(h[i-1] > h[i]) {
				flag = false;
				break;
			}
		}

		System.out.print(flag ? "Yes" : "No");
		sc.close();
	}
} Main
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] h = new int[n];
		boolean flag = true;

		for(int i = 0; i < n; i++) h[i] = sc.nextInt();

		h[0]--;
		for(int i = 1; i < n; i++) {
			if(h[i-1] < h[i]) {
				h[i]--;
			}else if(h[i-1] > h[i]) {
				flag = false;
				break;
			}
		}

		System.out.print(flag ? "Yes" : "No");
		sc.close();
	}
}