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(void){
   int i,n,x;
   string s;
   std::cin >> s;
   if(s[0]==s[1]){
       if(s[2]==s[3]&&s[2]!=s[0])std::cout << "Yes" << std::endl;
       else std::cout << "No" << std::endl;
   }
    else if(s[0]==s[2]){
       if(s[1]==s[3]&&s[1]!=s[0])std::cout << "Yes" << std::endl;
       else std::cout << "No" << std::endl;
   }
   else if(s[0]==s[3]){
       if(s[1]==s[2]&&s[1]!=s[0])std::cout << "Yes" << std::endl;
       else std::cout << "No" << std::endl;
   }
   else std::cout << "No" << std::endl;
}