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 s;
    cin >> s;
  	if (s == "ILIL")
      cout << "Yes";
    else if (s[0]==s[1] && s[0] != s[2])
    {
        if (s[2]==s[3])
            cout << "Yes";
        else cout << "No";
    }
    else if (s[0]==s[2] && s[0] != s[1])
    {
        if (s[1]==s[3])
            cout << "yes";
        else cout << "No";
    }
    else if (s[0]==s[3] && s[0] != s[1])
    {
        if (s[1]==s[2])
            cout <<  "Yes";
        else cout << "No";
    }
    else cout << "No";
}