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: Accepted)

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;

namespace AtCoder.ABC111 {
    class C {
        static void Main() => CustomMain();

        static int n;
        private static int[] a;

        static void Solve() {
            n = ReadInt();
            a = ReadIntArray();
            var a1 = new int[n / 2];
            var a2 = new int[n / 2];

            for (int i = 0; i < n; i++) {
                if (IsOdd(i)) {
                    a1[i / 2] = a[i];
                } else {
                    a2[i / 2] = a[i];
                }
            }

            var d1 = new Dictionary<int, int>();
            foreach (var v in a1) {
                if (d1.ContainsKey(v)) {
                    d1[v]++;
                } else {
                    d1.Add(v, 1);
                }
            }

            var d2 = new Dictionary<int, int>();
            foreach (var v in a2) {
                if (d2.ContainsKey(v)) {
                    d2[v]++;
                } else {
                    d2.Add(v, 1);
                }
            }

            var t1 = d1.OrderByDescending(x => x.Value).ToArray();
            var t2 = d2.OrderByDescending(x => x.Value).ToArray();

            if (t1[0].Key != t2[0].Key) {
                WriteAnswer(ChangeNum(t1[0].Key, t2[0].Key));
                return;
            }

            if (1 == t1.Length && 1 == t2.Length) {
                WriteAnswer(n / 2);
                return;
            }

            if (1 < t1.Length && 1 == t2.Length) {
                WriteAnswer(ChangeNum(t1[1].Key, t2[0].Key));
                return;
            }

            if (1 == t1.Length && 1 < t2.Length) {
                WriteAnswer(ChangeNum(t1[0].Key, t2[1].Key));
                return;
            }

            var ans = Math.Min(ChangeNum(t1[1].Key, t2[0].Key), ChangeNum(t1[0].Key, t2[1].Key));
            WriteAnswer(ans);
        }

        static int ChangeNum(int key1, int key2) {
            int res = 0;
            for (int i = 0; i < n; i++) {
                if (IsOdd(i)) {
                    if (a[i] != key1) res++;
                } else {
                    if (a[i] != key2) res++;
                }
            }

            return res;
        }

        static void CustomMain() {
#if DEBUG
            // ファイルからテストケースを読み込む
            global::Common.ChangeStdIn();
            // 時間計測
            var stopwatch = new Stopwatch();
            stopwatch.Start();
#endif
            // 出力高速化
            var streamWriter = new StreamWriter(Console.OpenStandardOutput()) {AutoFlush = false};
            Console.SetOut(streamWriter);
            // 回答
            Solve();
#if DEBUG
            stopwatch.Stop();
            Console.WriteLine(stopwatch.Elapsed);
#endif
            Console.Out.Flush();
        }

        static string ReadString() => Console.ReadLine().Trim();
        static int ReadInt() => int.Parse(ReadString());
        static long ReadLong() => long.Parse(ReadString());
        static float ReadFloat() => float.Parse(ReadString());

        static double ReadDouble => double.Parse(ReadString());

        static string[] ReadStringArray() => ReadString().Split(' ');
        static int[] ReadIntArray() => Array.ConvertAll(ReadString().Split(' '), int.Parse);
        static long[] ReadLongArray() => Array.ConvertAll(ReadString().Split(' '), long.Parse);
        static float[] ReadFloatArray() => Array.ConvertAll(ReadString().Split(' '), float.Parse);
        static double[] ReadDoubleArray() => Array.ConvertAll(ReadString().Split(' '), double.Parse);

        static T TypeConversion<T>(string s) {
            if (typeof(T) == typeof(int)) {
                return (T) Convert.ChangeType(int.Parse(s), typeof(T));
            } else if (typeof(T) == typeof(long)) {
                return (T) Convert.ChangeType(long.Parse(s), typeof(T));
            } else if (typeof(T) == typeof(double)) {
                return (T) Convert.ChangeType(double.Parse(s), typeof(T));
            } else {
                return (T) Convert.ChangeType(s, typeof(T));
            }
        }

        static void ReadMulti<T, U>(out T a, out U b) {
            var str = ReadStringArray();
            a = TypeConversion<T>(str[0]);
            b = TypeConversion<U>(str[1]);
        }

        static void ReadMulti<T, U, V>(out T a, out U b, out V c) {
            var str = ReadStringArray();
            a = TypeConversion<T>(str[0]);
            b = TypeConversion<U>(str[1]);
            c = TypeConversion<V>(str[2]);
        }

        static void WriteAnswer(object ans) => Console.WriteLine(ans);

        static bool IsOdd(long num) {
            return (num & 1) == 1;
        }

        static bool IsEven(long num) {
            return (num & 1) == 0;
        }
    }
}