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(input){
  input=input.trim().split('').sort();
  const ans=((input[0]!==input[1])?'No':
             (input[2]!==input[3])?'No':
             (input[0]===input[2])?'No':
             'Yes');
  console.log(ans);
})(require('fs').readFileSync('/dev/stdin','utf8'));