import java.util.Scanner;

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 = 0; i < (n - 1); i++) {
      if ((h[i + 1] - h[i]) < 0) {
        System.out.println("No");
        return;
      } else if (h[i + 1] > h[i]) {
        h[i + 1]--;
      }
    }

    System.out.println("Yes");

  }
} import java.util.Scanner; Scanner 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 = 0; i < (n - 1); i++) {
      if ((h[i + 1] - h[i]) < 0) {
        System.out.println("No");
        return;
      } else if (h[i + 1] > h[i]) {
        h[i + 1]--;
      }
    }

    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 = 0; i < (n - 1); i++) {
      if ((h[i + 1] - h[i]) < 0) {
        System.out.println("No");
        return;
      } else if (h[i + 1] > h[i]) {
        h[i + 1]--;
      }
    }

    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 = 0; i < (n - 1); i++) {
      if ((h[i + 1] - h[i]) < 0) {
        System.out.println("No");
        return;
      } else if (h[i + 1] > h[i]) {
        h[i + 1]--;
      }
    }

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

    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 = 0; i < (n - 1); i++) {
      if ((h[i + 1] - h[i]) < 0) {
        System.out.println("No");
        return;
      } else if (h[i + 1] > h[i]) {
        h[i + 1]--;
      }
    }

    System.out.println("Yes");

  }
} Main
import java.util.Scanner;

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 = 0; i < (n - 1); i++) {
      if ((h[i + 1] - h[i]) < 0) {
        System.out.println("No");
        return;
      } else if (h[i + 1] > h[i]) {
        h[i + 1]--;
      }
    }

    System.out.println("Yes");

  }
}