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: Accepted)

import java.util.Scanner;

public class Main{

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String S = sc.next();
		
		char A = S.charAt(0);
		char B = S.charAt(1);
		char C = S.charAt(2);
		char D = S.charAt(3);
		
		boolean ans = false;
		
		if (A==B) {
			if (C==D && A!=C)
				ans = true;
		}
		
		else if (A==C) {
			if (B==D && A!=B)
				ans = true;
		}
		
		else if (A==D) {
			if (B==C && A!=B)
				ans = true;
		}
		
		if (ans==false)
			System.out.println("No");
		else 
			System.out.println("Yes");
		sc.close();

	}

}