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 < h.length; i++) {
            h[i] = sc.nextInt();
        }
        boolean ok = true;
        for (int i = h.length - 2; i >= 0; i--) {
            if (h[i] - h[i + 1] == 1) {
                h[i]--;
            } else if (h[i] > h[i + 1]) {
                ok = false;
            }
        }
        if (ok) {
            System.out.println("Yes");
        } else {
            System.out.println("No");
        }
        sc.close();
    }
} 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 < h.length; i++) {
            h[i] = sc.nextInt();
        }
        boolean ok = true;
        for (int i = h.length - 2; i >= 0; i--) {
            if (h[i] - h[i + 1] == 1) {
                h[i]--;
            } else if (h[i] > h[i + 1]) {
                ok = false;
            }
        }
        if (ok) {
            System.out.println("Yes");
        } else {
            System.out.println("No");
        }
        sc.close();
    }
} 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 < h.length; i++) {
            h[i] = sc.nextInt();
        }
        boolean ok = true;
        for (int i = h.length - 2; i >= 0; i--) {
            if (h[i] - h[i + 1] == 1) {
                h[i]--;
            } else if (h[i] > h[i + 1]) {
                ok = false;
            }
        }
        if (ok) {
            System.out.println("Yes");
        } else {
            System.out.println("No");
        }
        sc.close();
    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] h = new int[n];
        for (int i = 0; i < h.length; i++) {
            h[i] = sc.nextInt();
        }
        boolean ok = true;
        for (int i = h.length - 2; i >= 0; i--) {
            if (h[i] - h[i + 1] == 1) {
                h[i]--;
            } else if (h[i] > h[i + 1]) {
                ok = false;
            }
        }
        if (ok) {
            System.out.println("Yes");
        } else {
            System.out.println("No");
        }
        sc.close();
    } 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 < h.length; i++) {
            h[i] = sc.nextInt();
        } int i = 0; int i = 0; i 0 i < h.length i h.length h h.length i++ i++ i {
            h[i] = sc.nextInt();
        } {
            h[i] = sc.nextInt();
        } h[i] = sc.nextInt() h[i] h i sc.nextInt() sc.nextInt sc boolean ok = true; ok true for (int i = h.length - 2; i >= 0; i--) {
            if (h[i] - h[i + 1] == 1) {
                h[i]--;
            } else if (h[i] > h[i + 1]) {
                ok = false;
            }
        } int i = h.length - 2; int i = h.length - 2; i h.length - 2 h.length h h.length 2 i >= 0 i 0 i-- i-- i {
            if (h[i] - h[i + 1] == 1) {
                h[i]--;
            } else if (h[i] > h[i + 1]) {
                ok = false;
            }
        } {
            if (h[i] - h[i + 1] == 1) {
                h[i]--;
            } else if (h[i] > h[i + 1]) {
                ok = false;
            }
        } if (h[i] - h[i + 1] == 1) {
                h[i]--;
            } else if (h[i] > h[i + 1]) {
                ok = false;
            } h[i] - h[i + 1] == 1 h[i] - h[i + 1] h[i] h i h[i + 1] h i + 1 i 1 1 {
                h[i]--;
            } h[i]-- h[i] h i if (h[i] > h[i + 1]) {
                ok = false;
            } h[i] > h[i + 1] h[i] h i h[i + 1] h i + 1 i 1 {
                ok = false;
            } ok = false ok false if (ok) {
            System.out.println("Yes");
        } else {
            System.out.println("No");
        } ok {
            System.out.println("Yes");
        } System.out.println("Yes") System.out.println System.out System System.out "Yes" {
            System.out.println("No");
        } System.out.println("No") System.out.println System.out System System.out "No" sc.close() sc.close sc 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 < h.length; i++) {
            h[i] = sc.nextInt();
        }
        boolean ok = true;
        for (int i = h.length - 2; i >= 0; i--) {
            if (h[i] - h[i + 1] == 1) {
                h[i]--;
            } else if (h[i] > h[i + 1]) {
                ok = false;
            }
        }
        if (ok) {
            System.out.println("Yes");
        } else {
            System.out.println("No");
        }
        sc.close();
    }
} 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 < h.length; i++) {
            h[i] = sc.nextInt();
        }
        boolean ok = true;
        for (int i = h.length - 2; i >= 0; i--) {
            if (h[i] - h[i + 1] == 1) {
                h[i]--;
            } else if (h[i] > h[i + 1]) {
                ok = false;
            }
        }
        if (ok) {
            System.out.println("Yes");
        } else {
            System.out.println("No");
        }
        sc.close();
    }
} 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 < h.length; i++) {
            h[i] = sc.nextInt();
        }
        boolean ok = true;
        for (int i = h.length - 2; i >= 0; i--) {
            if (h[i] - h[i + 1] == 1) {
                h[i]--;
            } else if (h[i] > h[i + 1]) {
                ok = false;
            }
        }
        if (ok) {
            System.out.println("Yes");
        } else {
            System.out.println("No");
        }
        sc.close();
    }
}