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

int main(){
  string s;
  cin>>s;
  vector<char>vec;
  for(int i=0;i<s.length();i++){
    sort(vec.begin(),vec.end());
    if(!binary_search(vec.begin(),vec.end(),s[i])){
        vec.push_back(s[i]);
    }
  }
  if(vec.size()==2){
    cout<<"Yes"<<endl;
  }else{
    cout<<"No"<<endl;
  }
  return 0;
}