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.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        var n = int.Parse(Console.ReadLine());
        var s = Console.ReadLine().Split(' ');
        var d = new int[n];
        for (int i = 0; i < n; i++)
        {
            d[i] = int.Parse(s[i]);
        }

        var maps = new[] {
            new Dictionary<int, int>(),
            new Dictionary<int, int>()
        };

        for (int i = 0; i < d.Length; i++)
        {
            if (maps[i % 2].ContainsKey(d[i]))
            {
                maps[i % 2][d[i]]++;
            }
            else
            {
                maps[i % 2][d[i]] = 1;
            }
        }

        var maxs = new[] {
            new[] { new KeyValuePair<int, int>(), new KeyValuePair<int, int>(), },
            new[] { new KeyValuePair<int, int>(), new KeyValuePair<int, int>(), },
        };

        for (int i = 0; i < 2; i++)
        {
            var max = maxs[i];
            var map = maps[i];

            foreach (var item in map)
            {
                if (max[1].Value < item.Value)
                {
                    if (max[0].Value < item.Value)
                    {
                        max[1] = max[0];
                        max[0] = item;
                    }
                    else
                    {
                        max[1] = item;
                    }
                }
            }
        }

        var dx = new[] { 0, 0, 1 };
        var dy = new[] { 0, 1, 0 };

        var ans = int.MaxValue;

        for (int i = 0; i < 3; i++)
        {
            if (maxs[0][dx[i]].Key != maxs[1][dy[i]].Key)
            {
                ans = Math.Min(ans, maxs[0][dx[i]].Value + maxs[1][dy[i]].Value);
            }
        }

        Console.WriteLine(n - ans);
    }
}