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<set>
using namespace std;
int main(){
  	string s;
  	cin>>s;
  	set<char>a;
  	a.insert(s[0]);
  	a.insert(s[1]);
  	a.insert(s[2]);
  	a.insert(s[3]);
  	if(a.size()==2)
        cout<<"Yes"<<endl;
    else cout<<"No"<<endl;
	return 0;
}