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 <iostream>
#include <string>
#include <algorithm>
#include <numeric>
#include <queue>
#include <utility>
#include <cmath>
#include <iomanip>
#include <map>
using namespace std;

#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)
#define ALL(a)  (a).begin(),(a).end()

typedef long long lint;
typedef pair<int,int> P;


int main() {
    string S;
    cin >> S;

    string ans="No";

    map<char,int> mp;

    REP(i,4){
    	char t;
    	t= S[i];
    	mp[t]++;

    }


    if(mp.size()!=2){
    	cout << ans << endl;
    	return 0;
    }

    char t=S[0];
    if(mp[t]!=2){
    	cout << ans << endl;
    	return 0;
    }

    ans = "Yes";
	cout << ans << endl;

}