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: Runtime Error)

function main(input) {
  
var a = input.substr( 0,1 );
  var b = input.substr( 1,1 );
  var c = input.substr( 2,1 );
  var d = input.substr( 3,1 );
  
 var str = input;
  
 var str = [a,b,c,d];

 str.sort();
  
  var a = str[0];
  var b = str[1];
  var c = str[2];
  var d = str[3];
  
  var f = 0；
  　if (a == b) {
    if (a !== c) ( c == d){var f 1;}
   }
  if (f == 1){console.log('Yes')}else{console.log('NO');}
}
main(require('fs').readFileSync("/dev/stdin","ut8"));