Problem:
Score : 300 points

Problem Statement

A sequence a_1,a_2,... ,a_n is said to be /\/\/\/ when the following conditions are satisfied:

For each i = 1,2,..., n-2, a_i = a_{i+2}.

Exactly two different numbers appear in the sequence.

You are given a sequence v_1,v_2,...,v_n whose length is even.
We would like to make this sequence /\/\/\/ by replacing some of its elements.
Find the minimum number of elements that needs to be replaced.

Constraints

2 \leq n \leq 10^5

n is even.

1 \leq v_i \leq 10^5

v_i is an integer.

Input

Input is given from Standard Input in the following format:

n
v_1 v_2 ... v_n

Output

Print the minimum number of elements that needs to be replaced.

Sample Input 1

4
3 1 3 2

Sample Output 1

1

The sequence 3,1,3,2 is not /\/\/\/, but we can make it /\/\/\/ by replacing one of its elements: for example, replace the fourth element to make it 3,1,3,1.

Sample Input 2

6
105 119 105 119 105 119

Sample Output 2

0

The sequence 105,119,105,119,105,119 is /\/\/\/.

Sample Input 3

4
1 1 1 1

Sample Output 3

2

The elements of the sequence 1,1,1,1 are all the same, so it is not /\/\/\/.

Solution in C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

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

namespace AtCoder_BeginerContest
{
    class Program
    {

        static void Main(string[] args)
        {
            int n = int.Parse(Console.ReadLine());
            string str = Console.ReadLine();
            var progression = str.Split(' ').Select(int.Parse);
            var twoProgressions = progression.Select((p, i) => new { Content = p, Index = i });
            var evenProgression = twoProgressions.Where(p => p.Index % 2 == 0).Select(p => p.Content);
            var oddProgression = twoProgressions.Where(p => p.Index % 2 == 1).Select(p => p.Content);

            if (evenProgression.Count() == oddProgression.Count())
            {
                int index = 0;
                var flag = true;

                foreach (var ep in evenProgression)
                {
                    if (ep != oddProgression.ElementAt(index))
                    {
                        flag = false;
                        break;
                    }
                    index++;
                }

                if (flag)
                {
                    Console.WriteLine(n / 2);
                    return;
                }
            }

            int modNumEvenProg = evenProgression.Mode();
            int modNumOddProg = oddProgression.Mode();

            // 修正する箇所の数を計測
            int count;
            count = evenProgression.Count(ep => ep != modNumEvenProg);
            count += oddProgression.Count(op => op != modNumOddProg);
            Console.WriteLine(count);
        }
    }

    public static class MyExtension 
    {
        public static int Mode(this IEnumerable<int> progression)
        {
            var NumsOfElements = new Dictionary<int, int>();
            progression.Distinct().ToList().ForEach(p =>
            {
                NumsOfElements.Add(p, 0);
            });
            progression.ToList().ForEach(p =>
            {
                NumsOfElements[p]++;
            });
            var elements = NumsOfElements.OrderByDescending(noe => noe.Value);
            return elements.ElementAt(0).Key;
        }
    }
}