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: Time Limit Exceeded)

using System;
class Program
{
    static void Main(string[] args)
    {
        int n = int.Parse(Console.ReadLine());
        string[] vs = Console.ReadLine().Split(' ');
        int[] v = new int[n];
        for(int i = 0; i < n; i++) { v[i] = int.Parse(vs[i]); }
        int[] v_odd = new int[n / 2];
        int[] v_even = new int[n / 2];
        for(int i = 0; i < n/2; i++)
        {
            v_even[i] = v[i*2];
            v_odd[i] = v[i*2+1];

        }
        int ans = 0;
        int modecount_odd = Mode(n / 2, v_odd).count;
        int modecount_even = Mode(n / 2, v_even).count;
        int submodecount_even = Submode(n/2,v_even).subcount;
        int submodecount_odd = Submode(n/2,v_odd).subcount;
        if (Mode(n / 2, v_odd).mode != Mode(n / 2, v_even).mode)
        {
            ans = n - modecount_odd - modecount_even;
        }
        else if (modecount_odd >= modecount_even)
        {
            ans = n - modecount_odd - submodecount_even;
        }
        else {ans= n - modecount_even - submodecount_odd; }

        Console.WriteLine(ans);
       
       
     

    }
    struct modecount { public int mode;public int count; }
    static modecount Mode(int n,int[] v)//n個の数から最頻値を見つける
    {
        int[] num = new int[n];
        for (int i = 0; i < n; i++)
        {
            num[i] = v[i];
        }
        int mode= 0;
        int count = 0;
     
        int temp_count = 0;
        
        for (int i = 0; i < n; i++)
        {
            temp_count = 1;
            for(int j = i + 1; j < n; j++)
            {
                if (num[i] == num[j]) { temp_count++; }
            }
            if (temp_count > count) { count = temp_count;mode = num[i]; }
        }

        return new modecount { mode = mode, count = count };
    }
    struct submodecount { public int submode; public int subcount; }
    static submodecount Submode(int n, int[] v)//n個の数から最頻値を見つける
    {
        int[] num = new int[n];
        for (int i = 0; i < n; i++)
        {
            num[i] = v[i];
        }
        int mode = 0;
        int count = 0;

        int temp_count = 0;
        int subcnt = 0;
        int submode = 0;
        for (int i = 0; i < n; i++)
        {
            temp_count = 1;
            for (int j = i + 1; j < n; j++)
            {
                if (num[i] == num[j]) { temp_count++; }
            }
            if (temp_count > count) {
                subcnt = count;
                count = temp_count;
                submode = mode;
                mode = num[i]; }
        }

        return new submodecount { submode = submode, subcount = subcnt };
    }
}