using System;
using System.Collections;

public abstract class IntSequence: IEnumerable {
  public abstract IEnumerator GetEnumerator();
  public abstract int? Min {get;}
  public abstract int? Max {get;}
}    

public class IntInterval: IntSequence{

  private int from, to;

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

  public override int? Min{
    get {return Math.Min(from,to);}
  }

  public override int? Max{
    get {return Math.Max(from,to);}
  }
    
  public override IEnumerator GetEnumerator (){
    if (from < to)
     for(int i = from; i <= to; i++)
       yield return i;
    else
     for(int i = from; i >= to; i--)
       yield return i;
  }

}     

public class IntSingular: IntSequence{

  private int it;

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

  public override int? Min{
    get {return it;}
  }

  public override int? Max{
    get {return it;}
  }

  public override IEnumerator GetEnumerator(){
    yield return it;
  }
}     


// Binary sequence: Exactly two subsequences.
public class IntCompSeq: IntSequence{

  private IntSequence s1, s2;

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

  public override int? Min{
    get {return (s1.Min < s2.Min) ? s1.Min : s2.Min;}
  }

  public override int? Max{
    get {return (s1.Max > s2.Max) ? s1.Max : s2.Max;}
  }

  public override IEnumerator GetEnumerator (){
    foreach(int i in s1)
      yield return i;
    foreach(int i in s2)
      yield return i;
  }

}