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: Accepted)

#include <iostream>
#include <algorithm>
#include <vector>
#include <string>

using namespace std;

int main(){
	string S;
	cin >> S;
	int flag1 = 0;
	int flag2 = 0;
	int flag3 = 0;
	if(S[0]==S[1] && S[2]==S[3] && S[0]!=S[2]){
		flag1 = 1;
	}
	if(S[0]==S[2] && S[1]==S[3] && S[0]!=S[1]){
		flag2 = 1;
	}
	if(S[0]==S[3] && S[1]==S[2] && S[0]!=S[1]){
		flag3 = 1;
	}
	if(flag1+flag2+flag3!=0){
		cout << "Yes";
	}
	else{
		cout << "No";
	}
}