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 <sstream>
#include <algorithm>
#include <string>
#include <vector>
#include <stack>
#include <set>
#include <queue>
#include <map>
#include <numeric>
#include <functional>
#include <math.h>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;

#define INF ((int)1e9)
#define INFLL ((ll)1e18)
#define MOD (1000000007LL)


int main(int argc, const char * argv[]) {
    ios_base::sync_with_stdio(false);
    string S;
    cin >> S;
    char ac[4];
    for (int i = 0; i < S.length(); ++i) {
        ac[i] = S[i];
    }
    sort(ac, ac + 4);
    if (ac[0] == ac[1] && ac[1] != ac[2] && ac[2] == ac[3]) {
        cout << "Yes" << endl;
    } else {
        cout << "No" << endl;
    }

    return 0;
}