using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var populationYears = new Dictionary<int,int>();

        var people = new Dictionary<int,int>();

        people.Add(1920, 2000);

        people.Add(1930, 1990);

        people.Add(1900, 2010);

        people.Add(1940, 2010);

        people.Add(1925, 1975);

        foreach (var person in people)

        {

            for (var i = person.Key; i <= person.Value; i++)

            {

                if (!populationYears.ContainsKey(i))

                {

                    populationYears.Add(i, 0);  

                }

                populationYears[i]++;

            }

        }

        populationYears.Where(y => y.Value == populationYears.Values.Max()).Select(popYear => popYear.Key).Dump();

    }

}