using System;

public class Program

{

    public abstract class PatternPrinter {

        private int patternLength;

        public PatternPrinter(int patternLength) {

        this.patternLength = patternLength;

        }

        public void Print() {

        Random rnd = new Random();

        int specialIndex = rnd.Next(patternLength);

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

            if (i == specialIndex)

                PrintSpecial();

            else {

                int roll = rnd.Next(2); 

                if (roll == 0) PrintNormal();

                else PrintVariant();

            }

        }

    }

    public abstract void PrintNormal();

    public abstract void PrintVariant();

    public abstract void PrintSpecial();

}

​

    public class RiverPattern: PatternPrinter{

        public RiverPattern(int patternLength) :base(patternLength){

        }

        public override void PrintNormal(){

            Console.Write("***O   O***" +"\n" +"***O   O***"+"\n" + "***O   O***"+"\n" + "***O   O***"+"\n");

        }

        public override void PrintVariant(){

            Console.Write("**O   O****" +"\n" + "*O   O*****" +"\n" + "**O    O***" +"\n" + "***O   O***"+"\n");

        }

        public override void PrintSpecial(){

            Console.Write("**O    O***" +"\n" + "*O      O**" +"\n" + "*O  OO   O*"+"\n"  + "*O  O    O*"+"\n"  + "**O     O**"+"\n");

        }

    }

    public static void Main()

    {

        RiverPattern river = new RiverPattern(10);

        river.Print();

    }

}