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>

using namespace std;

int main()
{
	// 入力
	string S;
	cin >> S;
	
	vector<string> sChar(S.length());
	
	for (int i = 0; i < S.length(); i++)
	{
		// 1文字ずつ格納
		sChar[i] = S.substr(i, 1);
	}
	
	bool isYes = false;
	if (sChar[0] == sChar[1])
	{
		if (sChar[2] == sChar[3])
		{
			isYes = true;
		}
	}
	else if (sChar[1] == sChar[2])
	{
		if (sChar[0] == sChar[3])
		{
			isYes = true;
		}
	}
	else if (sChar[0] == sChar[2])
	{
		if (sChar[1] == sChar[3])
		{
			isYes = true;
		}
	}
	
	
	if (isYes == true)
	{
		cout << "Yes" << endl;
	}
	else {
		cout << "No" << endl;
	}
	
	return 0;
}