using System;
using System.Collections.Generic;
using System.Linq;

public class Program
{
  public static void Main()
  {
    foreach (var i in Fibonacci().Take(20))
    {
      Console.WriteLine(i);
    }
  }

  private static IEnumerable<int> Fibonacci()
  {
    int current = 1, next = 1;

    while (true) 
    {
      yield return current;
      next = current + (current = next);
    }
  }
}