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'
function main(input) {
  input = input.trim().split('')
  let obj = {}
  for (let i = 0; i < 4; i++) {
    if (input[i] in obj) {
      obj[input[i]]++
    } else {
      obj[input[i]] = 1
    }
  }
  const ans = Object.keys(obj).length === 2 ? 'Yes' : 'No'
  console.log(ans)
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));