Problem:
Score : 100 points

Problem Statement

A string of length 6 consisting of lowercase English letters is said to be coffee-like if and only if its 3-rd and 4-th characters are equal and its 5-th and 6-th characters are also equal.

Given a string S, determine whether it is coffee-like.

Constraints

S is a string of length 6 consisting of lowercase English letters.

Input

Input is given from Standard Input in the following format:

S

Output

If S is coffee-like, print Yes; otherwise, print No.

Sample Input 1

sippuu

Sample Output 1

Yes

In sippuu, the 3-rd and 4-th characters are equal, and the 5-th and 6-th characters are also equal.

Sample Input 2

iphone

Sample Output 2

No

Sample Input 3

coffee

Sample Output 3

Yes

Solution in C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;
using static System.Math;
using System.Linq;
using System.Text;
 
class DandA {
    static void Main(string[] args) {
        string s = ReadLineStr();
        if (s.Substring(0,1) != s.Substring(1,1) && 
            s.Substring(0,1) != s.Substring(2,1) &&
            s.Substring(0,1) != s.Substring(3,1) &&
            s.Substring(0,1) != s.Substring(4,1) &&
            s.Substring(0,1) != s.Substring(5,1) &&
            s.Substring(1,1) != s.Substring(2,1) &&
            s.Substring(1,1) != s.Substring(3,1) &&
            s.Substring(1,1) != s.Substring(4,1) &&
            s.Substring(1,1) != s.Substring(5,1) &&
            s.Substring(2,1) == s.Substring(3,1) &&
            s.Substring(2,1) != s.Substring(4,1) &&
            s.Substring(2,1) != s.Substring(5,1) &&
            s.Substring(3,1) != s.Substring(4,1) &&
            s.Substring(3,1) != s.Substring(5,1) &&
            s.Substring(4,1) == s.Substring(5,1)) {
            Console.WriteLine("Yes");
        }else {
            Console.WriteLine("No");
        }
    }
 
    static string alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZ";
    static string[] salphabet = {"a","b","c","d","e","f","g","h","i","j"};
    static string[] strAry = new string[] {"L", "R", "U", "D"};
    static int[] intArray = new int[10];
    static List<int> intList = new List<int>();
    static Dictionary<int, long> myTable = new Dictionary<int, long>();
    static HashSet<int>[] rtnArrAb = null;
    static HashSet<int>[] rtnArrCd = null;
    static long[,] Combi = new long[2001,2001];
    static long div = 1000000007;
    static int[] atest = new int[] {1, 1, 1, 2, 1, 2, 1, 5, 2, 2, 1, 5, 1, 2, 1, 14, 1, 5, 1, 5, 2, 2, 1, 15, 2, 2, 5, 4, 1, 4, 1, 51};
  
    static private string ReadLineStr() {return Console.ReadLine();}
    static private int ReadLineInt() {return int.Parse(Console.ReadLine());}
    static private long ReadLineLong() {return long.Parse(Console.ReadLine());}
    static private double ReadLineDouble() {return double.Parse(Console.ReadLine());}
    static private decimal ReadLineDecimal() {return decimal.Parse(Console.ReadLine());}
    static private string[] ReadLineStrArray() {return Console.ReadLine().Trim().Split();}
    static private int[] ReadLineIntArray() {return Console.ReadLine().Trim().Split().Select(a => int.Parse(a)).ToArray();}
    static private long[] ReadLineLongArray() {return Console.ReadLine().Trim().Split().Select(a => long.Parse(a)).ToArray();}
    static private double[] ReadLineDoubleArray() {return Console.ReadLine().Trim().Split().Select(a => double.Parse(a)).ToArray();}
    static private decimal[] ReadLineDecimalArray() {return Console.ReadLine().Trim().Split().Select(a => decimal.Parse(a)).ToArray();}
    static private List<int> ReadLineIntList() {return Console.ReadLine().Trim().Split().Select(a => int.Parse(a)).ToList();}
    static private List<long> ReadLineLongList() {return Console.ReadLine().Trim().Split().Select(a => long.Parse(a)).ToList();}
    static private string[][] ReadMLineStrArray(int arg) { return new int[arg].Select(_ => Console.ReadLine().Split()).ToArray();}
    static private int[][] ReadMLineIntArray(int arg) { return new int[arg].Select(_ => Console.ReadLine().Split().Select(int.Parse).ToArray()).ToArray();}
 
    static private bool IsPrime(int num) {
        if (num < 2) return false;
        if (num == 2) return true;
        else if (num % 2 == 0) return false;
        double sqrtNum = Math.Sqrt(num);
        for (int i = 3; i <= sqrtNum; i += 2) {
            if (num % i == 0) return false;
        }
        return true;
    }
  
    static private string IntToNString(int x, int n) {
        var nstring = "";
        var numbers = new string[] { "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "a", "b", "c", "d", "e", "f" };
        int r = 1;
        int q = x;
        while (q > 0) {
            r = q % n;
            nstring += numbers[r];
            q = q / n;
        }
        return string.Join("",nstring.Reverse());
    }
    static private long Gcd(long m,long n){
        long temp;
        while(m % n != 0) {
            temp = n;
            n = m % n;
            m = temp;
        }
        return n;
    }
 
    static private long Combination(long n,long r){
        if(n < r) {return 0;}
        if(n == r || r == 0) {return 1;}
        else if(Combi[n,r] == 0) {
            Combi[n,r] = (Combination(n-1,r-1)+Combination(n-1,r)) % div;
        }
        return Combi[n,r];
    }
}