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();
    }

    sc.close();

    int prev = -999999; 

    for (int i = 0; i < N; i++) {

      if (prev <= H[i] - 1) {
        H[i]--;
        prev = H[i];
      } else if (prev <= H[i]) {
        prev = H[i];
      } else {
        System.out.println("No");
        return;
      }

    }

    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();
    }

    sc.close();

    int prev = -999999; 

    for (int i = 0; i < N; i++) {

      if (prev <= H[i] - 1) {
        H[i]--;
        prev = H[i];
      } else if (prev <= H[i]) {
        prev = H[i];
      } else {
        System.out.println("No");
        return;
      }

    }

    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();
    }

    sc.close();

    int prev = -999999; 

    for (int i = 0; i < N; i++) {

      if (prev <= H[i] - 1) {
        H[i]--;
        prev = H[i];
      } else if (prev <= H[i]) {
        prev = H[i];
      } else {
        System.out.println("No");
        return;
      }

    }

    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();
    }

    sc.close();

    int prev = -999999; 

    for (int i = 0; i < N; i++) {

      if (prev <= H[i] - 1) {
        H[i]--;
        prev = H[i];
      } else if (prev <= H[i]) {
        prev = H[i];
      } else {
        System.out.println("No");
        return;
      }

    }

    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 sc.close() sc.close sc int prev = -999999; prev -999999 999999 for (int i = 0; i < N; i++) {

      if (prev <= H[i] - 1) {
        H[i]--;
        prev = H[i];
      } else if (prev <= H[i]) {
        prev = H[i];
      } else {
        System.out.println("No");
        return;
      }

    } int i = 0; int i = 0; i 0 i < N i N i++ i++ i {

      if (prev <= H[i] - 1) {
        H[i]--;
        prev = H[i];
      } else if (prev <= H[i]) {
        prev = H[i];
      } else {
        System.out.println("No");
        return;
      }

    } {

      if (prev <= H[i] - 1) {
        H[i]--;
        prev = H[i];
      } else if (prev <= H[i]) {
        prev = H[i];
      } else {
        System.out.println("No");
        return;
      }

    } if (prev <= H[i] - 1) {
        H[i]--;
        prev = H[i];
      } else if (prev <= H[i]) {
        prev = H[i];
      } else {
        System.out.println("No");
        return;
      } prev <= H[i] - 1 prev H[i] - 1 H[i] H i 1 {
        H[i]--;
        prev = H[i];
      } H[i]-- H[i] H i prev = H[i] prev H[i] H i if (prev <= H[i]) {
        prev = H[i];
      } else {
        System.out.println("No");
        return;
      } prev <= H[i] prev H[i] H i {
        prev = H[i];
      } prev = H[i] prev H[i] H i {
        System.out.println("No");
        return;
      } System.out.println("No") System.out.println System.out System System.out "No" return; 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();
    }

    sc.close();

    int prev = -999999; 

    for (int i = 0; i < N; i++) {

      if (prev <= H[i] - 1) {
        H[i]--;
        prev = H[i];
      } else if (prev <= H[i]) {
        prev = H[i];
      } else {
        System.out.println("No");
        return;
      }

    }

    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();
    }

    sc.close();

    int prev = -999999; 

    for (int i = 0; i < N; i++) {

      if (prev <= H[i] - 1) {
        H[i]--;
        prev = H[i];
      } else if (prev <= H[i]) {
        prev = H[i];
      } else {
        System.out.println("No");
        return;
      }

    }

    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();
    }

    sc.close();

    int prev = -999999; 

    for (int i = 0; i < N; i++) {

      if (prev <= H[i] - 1) {
        H[i]--;
        prev = H[i];
      } else if (prev <= H[i]) {
        prev = H[i];
      } else {
        System.out.println("No");
        return;
      }

    }

    System.out.println("Yes");
    
  }

}