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();
        }
        int flag = h[n - 1];
        for (int i = n - 2; i >= 0; i--) {
            if (flag == h[i] - 1)
                flag = h[i] - 1;
            else if (flag > h[i] - 1)
                flag = h[i];
            else {
                System.out.println("No");
                System.exit(0);
            }
        }
        System.out.println("Yes");
    }
} 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();
        }
        int flag = h[n - 1];
        for (int i = n - 2; i >= 0; i--) {
            if (flag == h[i] - 1)
                flag = h[i] - 1;
            else if (flag > h[i] - 1)
                flag = h[i];
            else {
                System.out.println("No");
                System.exit(0);
            }
        }
        System.out.println("Yes");
    }
} 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();
        }
        int flag = h[n - 1];
        for (int i = n - 2; i >= 0; i--) {
            if (flag == h[i] - 1)
                flag = h[i] - 1;
            else if (flag > h[i] - 1)
                flag = h[i];
            else {
                System.out.println("No");
                System.exit(0);
            }
        }
        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();
        }
        int flag = h[n - 1];
        for (int i = n - 2; i >= 0; i--) {
            if (flag == h[i] - 1)
                flag = h[i] - 1;
            else if (flag > h[i] - 1)
                flag = h[i];
            else {
                System.out.println("No");
                System.exit(0);
            }
        }
        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 int flag = h[n - 1]; flag h[n - 1] h n - 1 n 1 for (int i = n - 2; i >= 0; i--) {
            if (flag == h[i] - 1)
                flag = h[i] - 1;
            else if (flag > h[i] - 1)
                flag = h[i];
            else {
                System.out.println("No");
                System.exit(0);
            }
        } int i = n - 2; int i = n - 2; i n - 2 n 2 i >= 0 i 0 i-- i-- i {
            if (flag == h[i] - 1)
                flag = h[i] - 1;
            else if (flag > h[i] - 1)
                flag = h[i];
            else {
                System.out.println("No");
                System.exit(0);
            }
        } {
            if (flag == h[i] - 1)
                flag = h[i] - 1;
            else if (flag > h[i] - 1)
                flag = h[i];
            else {
                System.out.println("No");
                System.exit(0);
            }
        } if (flag == h[i] - 1)
                flag = h[i] - 1;
            else if (flag > h[i] - 1)
                flag = h[i];
            else {
                System.out.println("No");
                System.exit(0);
            } flag == h[i] - 1 flag h[i] - 1 h[i] h i 1 flag = h[i] - 1 flag h[i] - 1 h[i] h i 1 if (flag > h[i] - 1)
                flag = h[i];
            else {
                System.out.println("No");
                System.exit(0);
            } flag > h[i] - 1 flag h[i] - 1 h[i] h i 1 flag = h[i] flag h[i] h i {
                System.out.println("No");
                System.exit(0);
            } System.out.println("No") System.out.println System.out System System.out "No" System.exit(0) System.exit System 0 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) {
        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();
        }
        int flag = h[n - 1];
        for (int i = n - 2; i >= 0; i--) {
            if (flag == h[i] - 1)
                flag = h[i] - 1;
            else if (flag > h[i] - 1)
                flag = h[i];
            else {
                System.out.println("No");
                System.exit(0);
            }
        }
        System.out.println("Yes");
    }
} 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();
        }
        int flag = h[n - 1];
        for (int i = n - 2; i >= 0; i--) {
            if (flag == h[i] - 1)
                flag = h[i] - 1;
            else if (flag > h[i] - 1)
                flag = h[i];
            else {
                System.out.println("No");
                System.exit(0);
            }
        }
        System.out.println("Yes");
    }
} 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();
        }
        int flag = h[n - 1];
        for (int i = n - 2; i >= 0; i--) {
            if (flag == h[i] - 1)
                flag = h[i] - 1;
            else if (flag > h[i] - 1)
                flag = h[i];
            else {
                System.out.println("No");
                System.exit(0);
            }
        }
        System.out.println("Yes");
    }
}