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;
  int abc[26]={0};
  cin >> s;
  int flag;
  for(int i=0;i<4;i++){
    flag =s.at(i)-'0';
    flag=flag%26;
    abc[flag]++;
  }
  flag =0;
  bool yeno = true;
  for(int i=0;i<26;i++){
    if(abc[i]==2) flag++;
  }
  if(flag != 2) yeno=false;

  if(yeno) cout << "Yes" << endl;
  else cout << "No" << endl;
}