using System;

using System.Collections;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        int[][] intervals = new int[][]{

          new int[] {0,30},

          new int[] {5, 10},

          new int[] {3, 9},

          new int[] {4, 28},

          new int[] {15,20}

        };

​

        /*int[][] intervals = new int[][]{

          new int[] {4,5},

          new int[] {2, 3},

          new int[] {2,4},

          new int[] {3,5}

        };*/

        SortedSet<int> minHeap = new SortedSet<int>();

​

        Array.Sort(intervals, (a, b) => (a[0].CompareTo(b[0])));

        minHeap.Add(intervals[0][1]);

        for (int i = 1; i < intervals.Length; i++)

        {

            if (intervals[i][0] >= minHeap.Min)

            {

                Console.WriteLine(intervals[i][0]);

                minHeap.Remove(minHeap.Min);

            }

​

            minHeap.Add(intervals[i][1]);

        }

        Console.WriteLine(minHeap.Count);

    }

}