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.*;
import static java.lang.Math.*;
import java.math.BigInteger;

public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		
		// 入力
		String s = sc.next();
		
		// 計算
		String result = "Yes";
		HashMap<Character, Integer> hm = new HashMap<Character, Integer>();
		for(int i = 0; i < s.length(); i++){
		    hm.put(s.charAt(i), hm.getOrDefault(s.charAt(i), 0) + 1);
		}
		for(Integer i : hm.values()){
		    if(i != 2) result = "No";
		}

		// 出力
		System.out.println(result);
	}
}