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();

        String str1 = S.substring(0, 1);
        String str2 = "";
        String str3 = "none";
        boolean hantei = false;
        for(int i = 1; i < S.length(); i++){
            if(str1.equals(S.substring(i, i+1))){
                hantei = true;
            }else{
                if(str2.equals("")){
                    str2 = S.substring(i, i+1);
                }else{
                    str3 = S.substring(i, i+1);
                }
            }
        }
        if(str2.equals(str3) && hantei){
            System.out.println("Yes");
        }else{
            System.out.println("No");
        }
    }
}