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 <string>
using namespace std;

int main() {
  string a;
  cin >> a;
  if (a[0] == a[1] && a[2] == a[3] && a[0] != a[2]){
    cout << "Yes" << endl;
  }
  else if (a[0] == a[2] && a[1] == a[3] && a[0] != a[1]){
    cout << "Yes" << endl;
  }
  else if (a[0] == a[3] && a[1] == a[2] && a[0] != a[1]){
    cout << "Yes" << endl;
  }
  else {cout << "No" << endl;
  }
}