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 list = input.split("");
    var data = {};
    for (var i = 0; i < list.length; i++){
        var key = list[i];
        if (data[key] == undefined) data[key] = 0;
        data[key]++;
    }
    if (Object.keys(data).length == 2 && data[Object.keys(data)[0]] == 2) {
        console.log("Yes");
    } else {
        console.log("No");
    }
}

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