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();
    }
    String ans = "Yes";
    h[0]--;
    for(int i = 1; i < n; i++) {
      if(h[i] > h[i - 1]) {
        h[i]--;
      } else if(h[i] == h[i - 1]) {
        
      } else {
        ans = "No";
        break;
      }
    }
    System.out.println(ans);
  }
} 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();
    }
    String ans = "Yes";
    h[0]--;
    for(int i = 1; i < n; i++) {
      if(h[i] > h[i - 1]) {
        h[i]--;
      } else if(h[i] == h[i - 1]) {
        
      } else {
        ans = "No";
        break;
      }
    }
    System.out.println(ans);
  }
} 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();
    }
    String ans = "Yes";
    h[0]--;
    for(int i = 1; i < n; i++) {
      if(h[i] > h[i - 1]) {
        h[i]--;
      } else if(h[i] == h[i - 1]) {
        
      } else {
        ans = "No";
        break;
      }
    }
    System.out.println(ans);
  } 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();
    }
    String ans = "Yes";
    h[0]--;
    for(int i = 1; i < n; i++) {
      if(h[i] > h[i - 1]) {
        h[i]--;
      } else if(h[i] == h[i - 1]) {
        
      } else {
        ans = "No";
        break;
      }
    }
    System.out.println(ans);
  } 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 String ans = "Yes"; ans "Yes" h[0]-- h[0] h 0 for(int i = 1; i < n; i++) {
      if(h[i] > h[i - 1]) {
        h[i]--;
      } else if(h[i] == h[i - 1]) {
        
      } else {
        ans = "No";
        break;
      }
    } int i = 1; int i = 1; i 1 i < n i n i++ i++ i {
      if(h[i] > h[i - 1]) {
        h[i]--;
      } else if(h[i] == h[i - 1]) {
        
      } else {
        ans = "No";
        break;
      }
    } {
      if(h[i] > h[i - 1]) {
        h[i]--;
      } else if(h[i] == h[i - 1]) {
        
      } else {
        ans = "No";
        break;
      }
    } if(h[i] > h[i - 1]) {
        h[i]--;
      } else if(h[i] == h[i - 1]) {
        
      } else {
        ans = "No";
        break;
      } 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(h[i] == h[i - 1]) {
        
      } else {
        ans = "No";
        break;
      } h[i] == h[i - 1] h[i] h i h[i - 1] h i - 1 i 1 {
        
      } {
        ans = "No";
        break;
      } ans = "No" ans "No" break; System.out.println(ans) System.out.println System.out System System.out ans 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();
    }
    String ans = "Yes";
    h[0]--;
    for(int i = 1; i < n; i++) {
      if(h[i] > h[i - 1]) {
        h[i]--;
      } else if(h[i] == h[i - 1]) {
        
      } else {
        ans = "No";
        break;
      }
    }
    System.out.println(ans);
  }
} 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();
    }
    String ans = "Yes";
    h[0]--;
    for(int i = 1; i < n; i++) {
      if(h[i] > h[i - 1]) {
        h[i]--;
      } else if(h[i] == h[i - 1]) {
        
      } else {
        ans = "No";
        break;
      }
    }
    System.out.println(ans);
  }
} 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();
    }
    String ans = "Yes";
    h[0]--;
    for(int i = 1; i < n; i++) {
      if(h[i] > h[i - 1]) {
        h[i]--;
      } else if(h[i] == h[i - 1]) {
        
      } else {
        ans = "No";
        break;
      }
    }
    System.out.println(ans);
  }
}