import 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];
	for (int i=0; i<n; i++) h[i] = sc.nextInt();
	boolean can = true;
	h[0]--;
	for (int i=1; i<n; i++) {
	    if (h[i] < h[i-1]) {
		can = false;
		break;
	    } else if (h[i] == h[i-1]) {
	    } else {
		h[i]--;
	    }
	}
	if (can) System.out.print("Yes");
	else { System.out.print("No"); }
    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args) {
	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();
	boolean can = true;
	h[0]--;
	for (int i=1; i<n; i++) {
	    if (h[i] < h[i-1]) {
		can = false;
		break;
	    } else if (h[i] == h[i-1]) {
	    } else {
		h[i]--;
	    }
	}
	if (can) System.out.print("Yes");
	else { System.out.print("No"); }
    }
} Main public static void main(String[] args) {
	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();
	boolean can = true;
	h[0]--;
	for (int i=1; i<n; i++) {
	    if (h[i] < h[i-1]) {
		can = false;
		break;
	    } else if (h[i] == h[i-1]) {
	    } else {
		h[i]--;
	    }
	}
	if (can) System.out.print("Yes");
	else { System.out.print("No"); }
    } 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();
	boolean can = true;
	h[0]--;
	for (int i=1; i<n; i++) {
	    if (h[i] < h[i-1]) {
		can = false;
		break;
	    } else if (h[i] == h[i-1]) {
	    } else {
		h[i]--;
	    }
	}
	if (can) System.out.print("Yes");
	else { System.out.print("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 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 boolean can = true; can true h[0]-- h[0] h 0 for (int i=1; i<n; i++) {
	    if (h[i] < h[i-1]) {
		can = false;
		break;
	    } else if (h[i] == h[i-1]) {
	    } else {
		h[i]--;
	    }
	} int i=1; int i=1; i 1 i<n i n i++ i++ i {
	    if (h[i] < h[i-1]) {
		can = false;
		break;
	    } else if (h[i] == h[i-1]) {
	    } else {
		h[i]--;
	    }
	} {
	    if (h[i] < h[i-1]) {
		can = false;
		break;
	    } else if (h[i] == h[i-1]) {
	    } else {
		h[i]--;
	    }
	} if (h[i] < h[i-1]) {
		can = false;
		break;
	    } else if (h[i] == h[i-1]) {
	    } else {
		h[i]--;
	    } h[i] < h[i-1] h[i] h i h[i-1] h i-1 i 1 {
		can = false;
		break;
	    } can = false can false break; if (h[i] == h[i-1]) {
	    } else {
		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 if (can) System.out.print("Yes");
	else { System.out.print("No"); } can System.out.print("Yes") System.out.print System.out System System.out "Yes" { System.out.print("No"); } System.out.print("No") System.out.print 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];
	for (int i=0; i<n; i++) h[i] = sc.nextInt();
	boolean can = true;
	h[0]--;
	for (int i=1; i<n; i++) {
	    if (h[i] < h[i-1]) {
		can = false;
		break;
	    } else if (h[i] == h[i-1]) {
	    } else {
		h[i]--;
	    }
	}
	if (can) System.out.print("Yes");
	else { System.out.print("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];
	for (int i=0; i<n; i++) h[i] = sc.nextInt();
	boolean can = true;
	h[0]--;
	for (int i=1; i<n; i++) {
	    if (h[i] < h[i-1]) {
		can = false;
		break;
	    } else if (h[i] == h[i-1]) {
	    } else {
		h[i]--;
	    }
	}
	if (can) System.out.print("Yes");
	else { System.out.print("No"); }
    }
} Main
import 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];
	for (int i=0; i<n; i++) h[i] = sc.nextInt();
	boolean can = true;
	h[0]--;
	for (int i=1; i<n; i++) {
	    if (h[i] < h[i-1]) {
		can = false;
		break;
	    } else if (h[i] == h[i-1]) {
	    } else {
		h[i]--;
	    }
	}
	if (can) System.out.print("Yes");
	else { System.out.print("No"); }
    }
}
