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: Wrong Answer)

#include <iostream>
using namespace std;
int main(void){
    // Your code here
    string s;
    cin>>s;
    int n=0;
    if(s[0]==s[1]){
        n++;
    }
    if(s[2]==s[3]){
        n++;
    }
    if(s[0]==s[3]){
        n++;
    }
    if(s[1]==s[2]){
        n++;
    }
    if(s[0]==s[2]){
        n++;
    }
    if(n==2){
        cout<<"Yes";
    }else{
        cout<<"No";
    }
    
    
    return 0;
}