Problem:
Score : 100 points

Problem Statement

You are given a 4-character string S consisting of uppercase English letters.
Determine if S consists of exactly two kinds of characters which both appear twice in S.

Constraints

The length of S is 4.

S consists of uppercase English letters.

Input

Input is given from Standard Input in the following format:

S

Output

If S consists of exactly two kinds of characters which both appear twice in S, print Yes; otherwise, print No.

Sample Input 1

ASSA

Sample Output 1

Yes

S consists of A and S which both appear twice in S.

Sample Input 2

STOP

Sample Output 2

No

Sample Input 3

FFEE

Sample Output 3

Yes

Sample Input 4

FREE

Sample Output 4

No

Solution in C# (Mono 4.6.2.0) (judge verdict: Accepted)

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

namespace AtCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            MainStream();
        }
        static void MainStream()
        {
            Scan sc = new Scan();
            write wr = new write();

            char[] s = sc.chararr;

            Array.Sort(s);

            if(s[0]==s[1] && s[2]==s[3] && s[0]!=s[2])
            {
                wr.wri("Yes");
            }
            else
            {
                wr.wri("No");
            }

        }


    }

    class Scan
    {
        public string str => Console.ReadLine();

        public string[] strarr => str.Split(' ');

        public long[] longarr => strarr.Select(long.Parse).ToArray();
        public int[] intarr => strarr.Select(int.Parse).ToArray();
        public char[] chararr => str.ToArray();


    }



    class write
    {
        public void wri<Type>(Type x)
        {
            Console.WriteLine(x);
        }
    }

    class Method
    {
        static public int max(params int[] nums)
        {

            int maxx = nums[0];
            for (int i = 1; i < nums.Length; i++)
            {
                maxx = Math.Max(maxx, nums[i]);
            }
            return maxx;
        }
    }
}