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;

string IsRepeat(string s){
    if(s.at(0)==s.at(1)&&s.at(1)!=s.at(2)&&s.at(2)==s.at(3)){
        return "Yes";
    }
    else if(s.at(0)==s.at(2)&&s.at(2)!=s.at(1)&&s.at(1)==s.at(3)){
        return "Yes";
    }
    else if(s.at(0)==s.at(3)&&s.at(3)!=s.at(1)&&s.at(1)==s.at(2)){
        return "Yes";
    }
    else{
        return "No";
    }
}

int main(){
    string s; cin >> s;
    cout << IsRepeat(s) << endl;
    return 0;
}