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)

// inputに入力データ全体が入る
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; 
// 0文字目から4文字分を指定
  
  
 var str = [a,b,c,d];
str.sort();
 
  
 var a= str[0];
  var b= str[1];
 var c= str[2];
  var d= str[3];
 //  console.log(a,b,c,d)
var f = 0;
  if (a == b) {
              if (a !==c) {if  ( c == d){var f = 1;}
                                        
                            }
  }
    
     if (f == 1){console.log('Yes')}else{console.log('No');}
  
}

  
  //*この行以降は編集しないでください（標準入出力から一度に読み込み、Mainを呼び出します）
Main(require("fs").readFileSync("/dev/stdin", "utf8"));