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<cstdio>
#include<iostream>
#include<iomanip>
#include<vector>
#include<cmath>
#include<algorithm>
#include<string>

using namespace std;

int main(){
    string s;
    cin >> s;

    //sort
    for(int i=0;i<3;i++){
      for(int j=i+1;j<4;j++){
        if(s[i]>s[j])
          swap(s[i],s[j]);
      }
    }

    //judge
    if(s[0]==s[1] && s[2] == s[3] && s[1] != s[2])
      cout << "Yes\n";
    else
      cout << "No\n";
    return 0;
}