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 b = true;

        for (int i=n-1;i>=0&&b;i--){
            while (i>0&&h[i-1]<=h[i])i--;
            if (i>0)h[i-1]--;
            if (i>0&&h[i-1]>h[i])b=false;
        }
        if (b)System.out.println("Yes");
        else System.out.println("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 b = true;

        for (int i=n-1;i>=0&&b;i--){
            while (i>0&&h[i-1]<=h[i])i--;
            if (i>0)h[i-1]--;
            if (i>0&&h[i-1]>h[i])b=false;
        }
        if (b)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];
        for (int i=0;i<n;i++)h[i]=sc.nextInt();
        boolean b = true;

        for (int i=n-1;i>=0&&b;i--){
            while (i>0&&h[i-1]<=h[i])i--;
            if (i>0)h[i-1]--;
            if (i>0&&h[i-1]>h[i])b=false;
        }
        if (b)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];
        for (int i=0;i<n;i++)h[i]=sc.nextInt();
        boolean b = true;

        for (int i=n-1;i>=0&&b;i--){
            while (i>0&&h[i-1]<=h[i])i--;
            if (i>0)h[i-1]--;
            if (i>0&&h[i-1]>h[i])b=false;
        }
        if (b)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 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 b = true; b true for (int i=n-1;i>=0&&b;i--){
            while (i>0&&h[i-1]<=h[i])i--;
            if (i>0)h[i-1]--;
            if (i>0&&h[i-1]>h[i])b=false;
        } int i=n-1; int i=n-1; i n-1 n 1 i>=0&&b i>=0 i 0 b i-- i-- i {
            while (i>0&&h[i-1]<=h[i])i--;
            if (i>0)h[i-1]--;
            if (i>0&&h[i-1]>h[i])b=false;
        } {
            while (i>0&&h[i-1]<=h[i])i--;
            if (i>0)h[i-1]--;
            if (i>0&&h[i-1]>h[i])b=false;
        } while (i>0&&h[i-1]<=h[i])i--; i>0&&h[i-1]<=h[i] i>0 i 0 h[i-1]<=h[i] h[i-1] h i-1 i 1 h[i] h i i-- i if (i>0)h[i-1]--; i>0 i 0 h[i-1]-- h[i-1] h i-1 i 1 if (i>0&&h[i-1]>h[i])b=false; i>0&&h[i-1]>h[i] i>0 i 0 h[i-1]>h[i] h[i-1] h i-1 i 1 h[i] h i b=false b false if (b)System.out.println("Yes");
        else System.out.println("No"); b System.out.println("Yes") System.out.println System.out System System.out "Yes" 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];
        for (int i=0;i<n;i++)h[i]=sc.nextInt();
        boolean b = true;

        for (int i=n-1;i>=0&&b;i--){
            while (i>0&&h[i-1]<=h[i])i--;
            if (i>0)h[i-1]--;
            if (i>0&&h[i-1]>h[i])b=false;
        }
        if (b)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];
        for (int i=0;i<n;i++)h[i]=sc.nextInt();
        boolean b = true;

        for (int i=n-1;i>=0&&b;i--){
            while (i>0&&h[i-1]<=h[i])i--;
            if (i>0)h[i-1]--;
            if (i>0&&h[i-1]>h[i])b=false;
        }
        if (b)System.out.println("Yes");
        else System.out.println("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 b = true;

        for (int i=n-1;i>=0&&b;i--){
            while (i>0&&h[i-1]<=h[i])i--;
            if (i>0)h[i-1]--;
            if (i>0&&h[i-1]>h[i])b=false;
        }
        if (b)System.out.println("Yes");
        else System.out.println("No");
    }
}
