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 Java8 (OpenJDK 1.8.0) (judge verdict: Wrong Answer)

import java.util.Scanner;

public class Main {
	public static void main(String[] args)
	{
		 Scanner sc = new Scanner(System.in);
	     
		 String S = sc.next();
		 
		 char[] ch = new char[4];
		 for(int a=0;a<ch.length;++a)
		 {
			 ch[a] =S.charAt(a);
		 }
		 
		 int index=0;

		 for(int q=0;q<S.length()-1;++q)
		 {
			 for(int w=q+1;w<S.length();++w)
			 {
				 if(ch[q] == ch[w])
				 {
					 ++index;
				 }
			 }
	/*		 if(index==0||index==2||index==3)
			 {
				 System.out.println("NO");
				 break;
			 }*/
		 }
		 if(index==2)
		 {
			 System.out.println("YES");
		 }
		 else
			 System.out.println("NO");
	}
	}