using System;

public interface Visitor{
  int Visit (IntInterval iv);
  int Visit (IntSingular iv);
  int Visit (IntCompSeq iv);
}    


public abstract class IntSequence {
  public abstract int Accept(Visitor v);
}     


public class IntInterval: IntSequence{

  private int from, to;

  public IntInterval(int from, int to){
    this.from = from;
    this.to = to;
  }

  public int From{
    get{return from;}
  }

  public int To{
    get{return to;}
  }

  public override int Accept(Visitor v){
    return v.Visit(this);
  } 
}      

public class IntSingular: IntSequence{

  private int it;

  public IntSingular(int it){
    this.it = it;
  }

  public int TheInt{
     get{return it;}
  }

  public override int Accept(Visitor v){
    return v.Visit(this);
  } 
}     


public class IntCompSeq: IntSequence{

  private IntSequence s1, s2;  // Binary sequence: Exactly two subsequences.

  public IntCompSeq(IntSequence s1, IntSequence s2) {
    this.s1 = s1;
    this.s2 = s2;
  }

  public IntSequence First{
    get{return s1;}
  }

  public IntSequence Second{
    get{return s2;}
  }

  public override int Accept(Visitor v){
    return v.Visit(this);
  } 
}         

public class MinVisitor: Visitor{
  public int Visit (IntInterval iv){
    return Math.Min(iv.From, iv.To);
  }

  public int Visit (IntSingular iv){
    return iv.TheInt;
  }

  public int Visit (IntCompSeq iv){
    return Math.Min(iv.First.Accept(this), 
                    iv.Second.Accept(this));
  }
}    

public class MaxVisitor: Visitor{
  public int Visit (IntInterval iv){
    return Math.Max(iv.From, iv.To);
  }

  public int Visit (IntSingular iv){
    return iv.TheInt;
  }

  public int Visit (IntCompSeq iv){
    return Math.Max(iv.First.Accept(this), 
                    iv.Second.Accept(this));
  }
}    

public class SumVisitor: Visitor{
  public int Visit (IntInterval iv){
    int res = 0;
    int lower = Math.Min(iv.From,iv.To),
        upper = Math.Max(iv.From,iv.To);

    for (int i = lower; i <= upper; i++) 
       res += i;
    return res;
  }

  public int Visit (IntSingular iv){
    return iv.TheInt;
  }

  public int Visit (IntCompSeq iv){
    return (iv.First.Accept(this) + 
            iv.Second.Accept(this));
  }
}