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){
        new Main().run();
    }

    private void run() {
        Scanner scanner = new Scanner(System.in);
        byte[] X = scanner.next().getBytes();
        int ok = 0;
        if(X[0] == X[1]) ok++;
        if(X[0] == X[2]) ok++;
        if(X[0] == X[3]) ok++;
        if(X[1] == X[2]) ok++;
        if(X[1] == X[3]) ok++;
        if(X[2] == X[3]) ok++;

        if(ok == 2) {
            System.out.println("Yes");
        } else {
            System.out.println("No");
        }

    }
}