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 C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <iostream>
#include <string>

using namespace std;

int main(){
    string S;
    //Sを定義
    char A;
    //Aを定義
    char B;
    //Bを定義
    bool isgood = true;
    if (S[A] == S[B]) isgood = false;
    if (S[B] == S[A]) isgood = false;
    bool duplicategooda = true;
    if (S[A] == S[A]) duplicategooda = false;
    if (S[B] == S[B]) duplicategooda = false;
    bool duplicategoodb = true;
    if (S[B] == S[A]) duplicategoodb = false;
    if (S[A] == S[B]) duplicategoodb = false;
    bool duplicategoodc = true;
    if (S[A] == S[B]) duplicategoodb = false;

    if (isgood){
        cout << "Yes" << endl;
    } else if(duplicategooda && duplicategoodb){
        cout << "Yes" << endl;
    } else if(duplicategoodb && duplicategooda){
        cout << "Yes" << endl;
    } else if(duplicategoodc &&duplicategoodc){
        cout << "Yes" << endl;
    } else {
        cout << "No" << endl;
    }
}