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 <cmath>
#include <iostream>
#include <functional>
#include <string>
#include <sstream>
#include <vector>
#include <algorithm>
#include <stdio.h>
using namespace std;

int main(){    
  string S;
  char a,b,acount=0,bcount=0;

  cin >> S;

  a = S[0];
  b = S[1];

  for(int i=2;i<4;i++){
    if(S[i] == a){
      acount++;
    }
    if(S[i] == b){
      bcount++;
    }
  }
    if(acount == 1 && bcount == 1){
      cout << "Yes" << endl;
    }
    else{
      cout << "No" << endl;
    }
}