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# (.NET Core 3.1.201) (judge verdict: Accepted)


using System;
using System.Linq;

public class a{
 static void Main(){
   var misaki = Console.ReadLine();
   int count = 0;
   for(int i=0; i< misaki.Length;i++){
    if(misaki.Count(x=>x==misaki[i])==2){
     count++;
   }
  }
   Console.WriteLine(count==4?"Yes":"No");
 }
}