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 <map>
#include <string>
#include <iterator>

using namespace std;

int main() 
{
  map<char,int> L;
  string S;
  cin >> S;
  for(char s : S) {L[s]++;}
  
  if(L.size() == 2)
  {
    map<char,int> :: iterator i = L.begin();
    if((*i).second == 2){cout << "Yes";}
    else {cout << "No";}
  }
  else { cout << "No";}
  return 0;
}