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: Wrong Answer)

"use strict"

const main = lines => {

  lines[0] = [...lines[0]]
  
  let k = {}
  for (const val of lines[0]) k[val] = k[val] ? k[val] + 1 : 0
  
  let r = Object.keys(k).length > 2 ? 'No' : 'Yes'
  if (k[lines[0][0]] !== 2) r = 'No'
  
  console.log(r)
}

main(require('fs').readFileSync('/dev/stdin', 'utf8').split('\n'))