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.*;
 
public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        String first = s.substring(0,1);
        String second = s.substring(1,2);
        String third = s.substring(2,3);
        String forth = s.substring(3,4);
        if (first.equals(second)) {
            if (third.equals(forth)&& !first.equals(forth)) {
                
                System.out.println("YES");
                return;
            }
            System.out.println("NO");
            return;
        }
        
        if (first.equals(third)) {
            if (second.equals(forth)&& !first.equals(forth)) {
                
                System.out.println("YES");
                return;
            }
            System.out.println("NO");
            return;
        }
        
        if (first.equals(forth)) {
            if (second.equals(third)&& !first.equals(third)) {
                
                System.out.println("YES");
                return;
            }
            System.out.println("NO");
            return;
        }
        System.out.println("NO");
    }
}