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;
#define rep(i, n) for(int i = 0; i < n; i++)

int main(void){
    string s;
    int count[4] = {}, count_all = 0;

    cin >> s;
    
    rep(i, 4){
        rep(j, 4){
            if(s[i] == s[j])
                count[i]++;
        }
    }

    rep(i, 4){
        if(count[i] == 2)
            count_all++;
    }

    if(count_all == 4)
        puts("Yes");
    else
        puts("No");

    return 0;
}