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.Collections.Generic;
using System.Linq;

namespace Atcoder
{
    class Program
    {
        static void Main(string[] args)
        {


			//テンプレート
			//// 整数の入力
			//int a = int.Parse(Console.ReadLine());
			//// スペース区切りの整数の入力
			//string[] input = Console.ReadLine().Split(' ');
			//int b = int.Parse(input[0]);
			//int c = int.Parse(input[1]);
			//// 文字列の入力
			//string s = Console.ReadLine();
			////出力
			//Console.WriteLine(a + b + c + " " + s);

			string input = Console.ReadLine();
			char[] input_char = input.ToCharArray();
			var hash = input_char.Distinct().ToArray();

			if (input_char.Length == 4 && hash.Length == 2)
			{
				Console.WriteLine("Yes");
			}
			else
			{
				Console.WriteLine("No");
			}


        }
    }
}