Problem:
Score : 200 points

Problem Statement

Takahashi lives in another world. There are slimes (creatures) of 10000 colors in this world. Let us call these colors Color 1, 2, ..., 10000.

Takahashi has N slimes, and they are standing in a row from left to right. The color of the i-th slime from the left is a_i.
If two slimes of the same color are adjacent, they will start to combine themselves. Because Takahashi likes smaller slimes, he has decided to change the colors of some of the slimes with his magic.

Takahashi can change the color of one slime to any of the 10000 colors by one spell.
How many spells are required so that no slimes will start to combine themselves?

Constraints

2 \leq N \leq 100

1 \leq a_i \leq N

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
a_1 a_2 ... a_N

Output

Print the minimum number of spells required.

Sample Input 1

5
1 1 2 2 2

Sample Output 1

2

For example, if we change the color of the second slime from the left to 4, and the color of the fourth slime to 5, the colors of the slimes will be 1, 4, 2, 5, 2, which satisfy the condition.

Sample Input 2

3
1 2 1

Sample Output 2

0

Although the colors of the first and third slimes are the same, they are not adjacent, so no spell is required.

Sample Input 3

5
1 1 1 1 1

Sample Output 3

2

For example, if we change the colors of the second and fourth slimes from the left to 2, the colors of the slimes will be 1, 2, 1, 2, 1, which satisfy the condition.

Sample Input 4

14
1 2 2 3 3 3 4 4 4 4 1 2 3 4

Sample Output 4

4

Solution in C# (Mono 4.6.2.0) (judge verdict: Runtime Error)

using System;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Runtime.Remoting.Services;
using System.Text;

namespace ConsoleApplication1
{
    internal static class Program
    {
        public static void Main(string[] args)
        {
            var scanner = new StreamScanner(Console.OpenStandardInput());
            var n = scanner.Integer();
         
            var arr = new int[n];
            for (var i = 0; i < n; i++)
            {
                arr[i] = scanner.Integer();
            }

            var stables = new HashSet<int>(Enumerable.Range(0, n).Where(x =>
                x == 0 || arr[x] != arr[x - 1] && x == n - 1 || arr[x] != arr[x + 1]
            ));

            var score = 0;

            for (var i = 0; i < n - 1; i++)
            {
                if (stables.Contains(i)) continue;

                var j = i + 1;
                for (; j < n; j++)
                {
                    if (stables.Contains(j)) break;
                }

                var diff = j - i;
                if (diff == 1) score += 1;
                else if (diff % 2 == 0) score += diff / 2;
                else if (diff % 2 == 1) score += (diff - 1) / 2;
                i = j;
            }

            Console.WriteLine(score);
        }
    }
    
    
    // https://qiita.com/Camypaper/items/de6d576fe5513743a50e
    public class StreamScanner
    {   
        private readonly Stream stream;
        private readonly byte[] buf = new byte[1024];
        private int len, pos;
        private bool isEof = false;
        public bool IsEndOfStream => isEof;

        public StreamScanner(Stream stream) { this.stream = stream; }
        
        private byte Read()
        {
            if (isEof) throw new EndOfStreamException();
            if (pos >= len) {
                pos = 0;
                if ((len = stream.Read(buf, 0, 1024)) <= 0)
                {
                    isEof = true;
                    return 0;
                }
            }
            return buf[pos++];
        }
        
        public char Char() 
        {
            byte b = 0;
            do b = Read();
            while (b < 33 || 126 < b);
            return (char)b; 
        }
        
        public string Scan()
        {
            var sb = new StringBuilder();
            for (var b = Char(); b >= 33 && b <= 126; b = (char)Read())
                sb.Append(b);
            return sb.ToString();
        }
        
        public long Long()
        {
            long ret = 0; byte b = 0; var ng = false;
            do b = Read();
            while (b != '-' && (b < '0' || '9' < b));
            if (b == '-') { ng = true; b = Read(); }
            for (; true; b = Read())
            {
                if (b < '0' || '9' < b)
                    return ng ? -ret : ret;
                else ret = ret * 10 + b - '0';
            }
        }
        
        public int Integer() { return (int)Long(); }
        public double Double() { return double.Parse(Scan(), CultureInfo.InvariantCulture); }
    }
}