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: Wrong Answer)

function Main(input) {
  var cont = {
  	"list" : []
  };//含まれている英字のリスト
  for(var i = 0; i < input.length; i++){
    var tmp = input.slice(i, i + 1);
    if(cont.list.indexOf(tmp) == -1){
       cont.list.push(tmp);
    }
    if(cont[tmp] == null){
         cont[tmp] = 1;
    }else{
         cont[tmp]++;  
    }
  }
  for(var i = 0; i < cont.list.length; i++){
    if(cont[cont.list[i]] != 2){
       console.log("No");
      return;
       }
  }
  
  console.log("Yes");
}

Main(require("fs").readFileSync("/dev/stdin", "utf8"));