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 {
	Scanner sc = new Scanner(System.in);

	void a() {
		String s = sc.next();
		char c1 = s.charAt(0),c2 = 0;
		int c1cnt = 1,c2cnt = 0;
		for(int i = 1;i < s.length();i ++) {
			char c = s.charAt(i);
			if(c == c1) c1cnt++;
			else if(c != c2) {
				c2cnt = 1;
				c2 = c;
			}
			else if(c == c2) c2cnt++;
		}
		if(c1cnt == 2 && c2cnt == 2) System.out.println("Yes");
		else System.out.println("No");
	}
	public static void main(String[] args) {
		new Main().a();
	}

}