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 JavaScript (node.js v5.12) (judge verdict: Accepted)

"use strict";
    
const main = arg => {
    let text = arg.trim().split("");
  	let ans = "No";
  	// 全部同じだった時の処理
  	if(text.every(elm => { return elm == text[0]})){
    	ans = "No"; 
    } 
  	else if(
      (text[0] == text[1] && text[2] == text[3])
      ||
      (text[0] == text[2] && text[1] == text[3])
      ||
      (text[0] == text[3] && text[1] == text[2])
  	)
    {
    	ans = "Yes";
    }
  	console.log(ans);
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));