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.Integer.*;
//import static java.lang.Long.*;
//import static java.lang.Math.*;

public class Main {
	public static void main(String[] args) {
		int i,j;
		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		sc.close();
		String ans;
		int a = s.indexOf(s.charAt(0), 1);
		int b = -1;
		if(a < 0) {
			ans = "No";
		} else {
			if(a == 1) {
				if(s.charAt(0) == s.charAt(2)) {
					ans = "No";
				} else {
					b = s.indexOf(s.charAt(2), 3);
				}
			} else {
				b = s.indexOf(s.charAt(1), 2);
			}
			if(b < 0) {
				ans = "No";
			} else {
				ans = "Yes";
			}
		}
		System.out.println(ans);
	}
}