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.Text;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
using static System.Console;
using static System.Math;

namespace AtCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            new Program().Solve(new ConsoleInput(Console.In, ' '));
        }

        public void Solve(ConsoleInput cin)
        {
            int n = cin.ReadInt;
            int[] v = new int[n];

            for (int i = 0; i < n; i++)
            {
                v[i] = cin.ReadInt;
            }

            Dictionary<int, int> odd = new Dictionary<int, int>();
            Dictionary<int, int> even = new Dictionary<int, int>();

            bool flip = true;
            for (int i = 0; i < n; i++)
            {
                if (flip)
                {
                    if (!odd.ContainsKey(v[i]))
                    {
                        odd.Add(v[i], 1);
                    }
                    else
                    {
                        odd[v[i]]++;
                    }
                }
                else
                {
                    if (!even.ContainsKey(v[i]))
                    {
                        even.Add(v[i], 1);
                    }
                    else
                    {
                        even[v[i]]++;
                    }
                }


                flip = !flip;
            }

            List<KeyValuePair<int, int>> orderedOdd = odd.OrderByDescending(x => x.Value).ToList<KeyValuePair<int, int>>();
            List<KeyValuePair<int, int>> orderedEven = even.OrderByDescending(x => x.Value).ToList<KeyValuePair<int, int>>();

            int result = 0;

            if(orderedOdd[0].Key != orderedEven[0].Key)
            {
                result = n - orderedOdd[0].Value - orderedEven[0].Value;
            }
            else if (orderedOdd.Count == 1 && orderedEven.Count > 1)
            {
                result = n - orderedOdd[0].Value - orderedEven[1].Value;
            }
            else if (orderedOdd.Count > 1 && orderedEven.Count == 1)
            {
                result = n - orderedOdd[1].Value - orderedEven[0].Value;
            }
            else if (orderedOdd.Count == 1 && orderedEven.Count == 1)
            {
                result = n / 2;
            }
            else
            {
                if(orderedOdd[1].Value > orderedEven[1].Value)
                {
                    result = n - orderedOdd[0].Value - orderedEven[1].Value;
                }
                else
                {
                    result = n - orderedOdd[1].Value - orderedEven[0].Value;
                }
            }

            Console.WriteLine(result);
        }
    }

    public class ConsoleInput
    {
        private readonly System.IO.TextReader _stream;
        private char _separator = ' ';
        private Queue<string> inputStream;

        public ConsoleInput(System.IO.TextReader stream, char separator = ' ')
        {
            this._separator = separator;
            this._stream = stream;
            inputStream = new Queue<string>();
        }

        public string Read
        {
            get
            {
                if (inputStream.Count != 0) return inputStream.Dequeue();
                string[] tmp = _stream.ReadLine().Split(_separator);
                for (int i = 0; i < tmp.Length; ++i)
                    inputStream.Enqueue(tmp[i]);
                return inputStream.Dequeue();
            }
        }

        public string ReadLine { get { return _stream.ReadLine(); } }
        public int ReadInt { get { return int.Parse(Read); } }
        public long ReadLong { get { return long.Parse(Read); } }
        public double ReadDouble { get { return double.Parse(Read); } }
        public string[] ReadStrArray(long N) { var ret = new string[N]; for (long i = 0; i < N; ++i) ret[i] = Read; return ret; }
        public int[] ReadIntArray(long N) { var ret = new int[N]; for (long i = 0; i < N; ++i) ret[i] = ReadInt; return ret; }
        public long[] ReadLongArray(long N) { var ret = new long[N]; for (long i = 0; i < N; ++i) ret[i] = ReadLong; return ret; }
    }
}