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 <bits/stdc++.h>
using namespace std;

int main(){
  int n = 4;
  vector<char > s(n);
  for ( int i = 0; i < n; i++ ) {
    cin >> s.at(i);
  }

  bool ans = false;
  if ( s.at(0) == s.at(1) && s.at(2) == s.at(3) ) ans = true;
  else if ( s.at(0) == s.at(2) && s.at(1) == s.at(3) ) ans = true;
  else if ( s.at(0) == s.at(3) && s.at(1) == s.at(2) ) ans = true;

  if ( ans ) cout << "Yes" << endl;
  else cout << "No" << endl;

  return 0;
}