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>
#include <vector>
#include <algorithm>
#include <math.h>

using namespace std;

int main() {
    string S;
    cin >> S;

    int count = 0;
    vector<char> vec;

    for (int i = 1; i < 4; i++)
    {
        if (S.at(0) == S.at(i))
        {
            count++;
        }
        else
        {
            vec.push_back(S.at(i));
        }
    }

    if (count == 1)
    {
        if (vec.size() == 2)
        {
            if (vec.at(0) == vec.at(1))
            {
                cout << "Yes" << endl;
            }
        }
        else
        {
            cout << "No" << endl;
        }
    }
    else
    {
        cout << "No" << endl;
    }
}