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: Runtime Error)

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

namespace ABC111_C
{
    class Program
    {
        static void Main(string[] args)
        {
            var n = int.Parse(Console.ReadLine());
            var v = Console.ReadLine().Split().Select(int.Parse).ToArray();

            if (v.Distinct().Count() == 1)
            {
                Console.WriteLine(n / 2);
                return;
            }

            var ve = new Dictionary<int, int>();
            var vo = new Dictionary<int, int>();

            for (int i = 0; i < v.Length; i++)
            {
                if (i % 2 == 0 || i == 0)
                {
                    if (ve.Keys.Contains(v[i]))
                    {
                        ve[v[i]]++;
                    }
                    else
                    {
                        ve.Add(v[i], 1);
                    }
                }
                else
                {
                    if (vo.Keys.Contains(v[i]))
                    {
                        vo[v[i]]++;
                    }
                    else
                    {
                        vo.Add(v[i], 1);
                    }
                }
            }

            bool twoTop = false;
            var veMost = ve.OrderByDescending(x => x.Value).Take(2).ToList();
            if (veMost.Count > 1 && veMost[0].Value == veMost[1].Value) twoTop = true;

            var voMost = vo.OrderByDescending(x => x.Value).Take(2).ToList();
            if (veMost.Count > 1 && voMost[0].Value == voMost[1].Value) twoTop = true;

            var cntve = ve.Select(x => x.Value).OrderByDescending(x => x).Skip(1).Sum();
            var cntvo = vo.Select(x => x.Value).OrderByDescending(x => x).Skip(1).Sum();

            if (veMost == voMost && !twoTop)
            {
                Console.WriteLine(cntve + n / 2 - cntvo);
            }
            else
            {
                Console.WriteLine(cntve + cntvo);
            }
        }
    }
}