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<iomanip>
#include<string>
#include<queue>
#include<vector>
using namespace std;
int main(){
  string s;
  cin>>s;
  char c[4];
  int syurui=0;
  for(int i=0;i<4;i++){
    c[i]=s.at(i);
  }

  for(int i=0;i<4;i++){
    int count=0;
    for(int j=i+1;j<4;j++){
      if(c[i]==c[j])count++;
    }
    if(count==1)syurui++;
  }
if(syurui==2)cout<<"Yes";
else cout<<"No";
return 0;
}