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();
    }

    for (int i = N-2; i >= 0; i--) {
      if (H[i] - H[i+1] > 1) {
        System.out.println("No");
        return;
      }
      if (H[i] > H[i+1]) {
        H[i]--;
      }
    }
    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();
    }

    for (int i = N-2; i >= 0; i--) {
      if (H[i] - H[i+1] > 1) {
        System.out.println("No");
        return;
      }
      if (H[i] > H[i+1]) {
        H[i]--;
      }
    }
    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();
    }

    for (int i = N-2; i >= 0; i--) {
      if (H[i] - H[i+1] > 1) {
        System.out.println("No");
        return;
      }
      if (H[i] > H[i+1]) {
        H[i]--;
      }
    }
    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();
    }

    for (int i = N-2; i >= 0; i--) {
      if (H[i] - H[i+1] > 1) {
        System.out.println("No");
        return;
      }
      if (H[i] > H[i+1]) {
        H[i]--;
      }
    }
    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 for (int i = N-2; i >= 0; i--) {
      if (H[i] - H[i+1] > 1) {
        System.out.println("No");
        return;
      }
      if (H[i] > H[i+1]) {
        H[i]--;
      }
    } int i = N-2; int i = N-2; i N-2 N 2 i >= 0 i 0 i-- i-- i {
      if (H[i] - H[i+1] > 1) {
        System.out.println("No");
        return;
      }
      if (H[i] > H[i+1]) {
        H[i]--;
      }
    } {
      if (H[i] - H[i+1] > 1) {
        System.out.println("No");
        return;
      }
      if (H[i] > H[i+1]) {
        H[i]--;
      }
    } if (H[i] - H[i+1] > 1) {
        System.out.println("No");
        return;
      } H[i] - H[i+1] > 1 H[i] - H[i+1] H[i] H i H[i+1] H i+1 i 1 1 {
        System.out.println("No");
        return;
      } System.out.println("No") System.out.println System.out System System.out "No" return; if (H[i] > H[i+1]) {
        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 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();
    }

    for (int i = N-2; i >= 0; i--) {
      if (H[i] - H[i+1] > 1) {
        System.out.println("No");
        return;
      }
      if (H[i] > H[i+1]) {
        H[i]--;
      }
    }
    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();
    }

    for (int i = N-2; i >= 0; i--) {
      if (H[i] - H[i+1] > 1) {
        System.out.println("No");
        return;
      }
      if (H[i] > H[i+1]) {
        H[i]--;
      }
    }
    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();
    }

    for (int i = N-2; i >= 0; i--) {
      if (H[i] - H[i+1] > 1) {
        System.out.println("No");
        return;
      }
      if (H[i] > H[i+1]) {
        H[i]--;
      }
    }
    System.out.println("Yes");
  }  
}