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 ary_counter(ary) {
  let c = 0;
  ary.forEach(a => ++c);
  return c;
}
 
function main(stdin) {
  const l = [];
  let res = 'Yes';
 
  for (let i = 0; i < 4; ++i) {    
    const c = stdin.charCodeAt(i);
    l[c] = l[c] || 0;
    ++l[c];
  }
 
  if (ary_counter(l) !== 2) res = 'No'; 
  
  console.log(res);
}
 
main(require('fs').readFileSync('/dev/stdin', 'utf8'));