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)

//
//  main.cpp
//  atcoderdemo
//
//  Created by apple on 2019/6/29.
//  Copyright © 2019 apple. All rights reserved.
//

#include <iostream>
#include <string.h>
#include <queue>
#define ll long long
using namespace std;
const int maxn = 1e5 + 5;
int a[maxn];
int sum[maxn];
int main(int argc, const char * argv[]) {
    string str;
    cin >> str;
    for(int i=0;i<str.size();i++){
        sum[str[i] - 'A']++;
    }
    for(int i=0;i<str.size();i++){
        if(sum[str[i] - 'A'] != 2){
            cout << "No";
            return 0;
        }
    }
    cout << "Yes";
    return 0;
}