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 possible = true;

		for (int i = 0; i < N; i++) {
			H[i] = sc.nextInt();
		}

		for (int i = 0; i < N - 1; i++) {
			if (H[i + 1] < H[i]) {
				H[i]--;
				if (H[i + 1] < H[i]) possible = false;
			} else if (1 <= i && 1 <= H[i] - H[i - 1]) {
				H[i]--;
			}
			if (1 <= i && H[i] < H[i - 1]) possible = false;
		}

		if (possible) {
			System.out.println("Yes");
		} else {
			System.out.println("No");
		}
	}
} 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 possible = true;

		for (int i = 0; i < N; i++) {
			H[i] = sc.nextInt();
		}

		for (int i = 0; i < N - 1; i++) {
			if (H[i + 1] < H[i]) {
				H[i]--;
				if (H[i + 1] < H[i]) possible = false;
			} else if (1 <= i && 1 <= H[i] - H[i - 1]) {
				H[i]--;
			}
			if (1 <= i && H[i] < H[i - 1]) possible = false;
		}

		if (possible) {
			System.out.println("Yes");
		} else {
			System.out.println("No");
		}
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int H[] = new int[N];
		boolean possible = true;

		for (int i = 0; i < N; i++) {
			H[i] = sc.nextInt();
		}

		for (int i = 0; i < N - 1; i++) {
			if (H[i + 1] < H[i]) {
				H[i]--;
				if (H[i + 1] < H[i]) possible = false;
			} else if (1 <= i && 1 <= H[i] - H[i - 1]) {
				H[i]--;
			}
			if (1 <= i && H[i] < H[i - 1]) possible = false;
		}

		if (possible) {
			System.out.println("Yes");
		} else {
			System.out.println("No");
		}
	} main {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int H[] = new int[N];
		boolean possible = true;

		for (int i = 0; i < N; i++) {
			H[i] = sc.nextInt();
		}

		for (int i = 0; i < N - 1; i++) {
			if (H[i + 1] < H[i]) {
				H[i]--;
				if (H[i + 1] < H[i]) possible = false;
			} else if (1 <= i && 1 <= H[i] - H[i - 1]) {
				H[i]--;
			}
			if (1 <= i && H[i] < H[i - 1]) possible = false;
		}

		if (possible) {
			System.out.println("Yes");
		} else {
			System.out.println("No");
		}
	} 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 possible = true; possible 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] = sc.nextInt() H[i] H i sc.nextInt() sc.nextInt sc for (int i = 0; i < N - 1; i++) {
			if (H[i + 1] < H[i]) {
				H[i]--;
				if (H[i + 1] < H[i]) possible = false;
			} else if (1 <= i && 1 <= H[i] - H[i - 1]) {
				H[i]--;
			}
			if (1 <= i && H[i] < H[i - 1]) possible = false;
		} int i = 0; int i = 0; i 0 i < N - 1 i N - 1 N 1 i++ i++ i {
			if (H[i + 1] < H[i]) {
				H[i]--;
				if (H[i + 1] < H[i]) possible = false;
			} else if (1 <= i && 1 <= H[i] - H[i - 1]) {
				H[i]--;
			}
			if (1 <= i && H[i] < H[i - 1]) possible = false;
		} {
			if (H[i + 1] < H[i]) {
				H[i]--;
				if (H[i + 1] < H[i]) possible = false;
			} else if (1 <= i && 1 <= H[i] - H[i - 1]) {
				H[i]--;
			}
			if (1 <= i && H[i] < H[i - 1]) possible = false;
		} if (H[i + 1] < H[i]) {
				H[i]--;
				if (H[i + 1] < H[i]) possible = false;
			} else if (1 <= i && 1 <= H[i] - H[i - 1]) {
				H[i]--;
			} H[i + 1] < H[i] H[i + 1] H i + 1 i 1 H[i] H i {
				H[i]--;
				if (H[i + 1] < H[i]) possible = false;
			} H[i]-- H[i] H i if (H[i + 1] < H[i]) possible = false; H[i + 1] < H[i] H[i + 1] H i + 1 i 1 H[i] H i possible = false possible false if (1 <= i && 1 <= H[i] - H[i - 1]) {
				H[i]--;
			} 1 <= i && 1 <= H[i] - H[i - 1] 1 <= i 1 i 1 <= H[i] - H[i - 1] 1 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 if (1 <= i && H[i] < H[i - 1]) possible = false; 1 <= i && H[i] < H[i - 1] 1 <= i 1 i H[i] < H[i - 1] H[i] H i H[i - 1] H i - 1 i 1 possible = false possible false if (possible) {
			System.out.println("Yes");
		} else {
			System.out.println("No");
		} possible {
			System.out.println("Yes");
		} System.out.println("Yes") System.out.println System.out System System.out "Yes" {
			System.out.println("No");
		} System.out.println("No") System.out.println System.out System System.out "No" 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 possible = true;

		for (int i = 0; i < N; i++) {
			H[i] = sc.nextInt();
		}

		for (int i = 0; i < N - 1; i++) {
			if (H[i + 1] < H[i]) {
				H[i]--;
				if (H[i + 1] < H[i]) possible = false;
			} else if (1 <= i && 1 <= H[i] - H[i - 1]) {
				H[i]--;
			}
			if (1 <= i && H[i] < H[i - 1]) possible = false;
		}

		if (possible) {
			System.out.println("Yes");
		} else {
			System.out.println("No");
		}
	}
} 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 possible = true;

		for (int i = 0; i < N; i++) {
			H[i] = sc.nextInt();
		}

		for (int i = 0; i < N - 1; i++) {
			if (H[i + 1] < H[i]) {
				H[i]--;
				if (H[i + 1] < H[i]) possible = false;
			} else if (1 <= i && 1 <= H[i] - H[i - 1]) {
				H[i]--;
			}
			if (1 <= i && H[i] < H[i - 1]) possible = false;
		}

		if (possible) {
			System.out.println("Yes");
		} else {
			System.out.println("No");
		}
	}
} 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 possible = true;

		for (int i = 0; i < N; i++) {
			H[i] = sc.nextInt();
		}

		for (int i = 0; i < N - 1; i++) {
			if (H[i + 1] < H[i]) {
				H[i]--;
				if (H[i + 1] < H[i]) possible = false;
			} else if (1 <= i && 1 <= H[i] - H[i - 1]) {
				H[i]--;
			}
			if (1 <= i && H[i] < H[i - 1]) possible = false;
		}

		if (possible) {
			System.out.println("Yes");
		} else {
			System.out.println("No");
		}
	}
}
