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 <functional>
#include <set>
#include <map>
#include <unordered_map>
#include <queue>
#include <deque>
#include <cmath>
#include <cstdio>

using namespace std;

typedef long long ll;

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

int main(int argc, char **argv)
{
    string S;
    cin >> S;

    char c = S[0];
    if (c == S[1]) {
        if (c != S[2] && S[2] == S[3]) cout << "Yes" << endl;
        else cout << "No" << endl;
    }
    else if (c == S[2]) {
        if (c != S[1] && S[1] == S[3]) cout << "Yes" << endl;
        else cout << "No" << endl;
    }
    else if (c == S[3]) {
        if (c != S[1] && S[1] == S[2]) cout << "Yes" << endl;
        else cout << "No" << endl;
    }
    else {
        cout << "No" << endl;
    }
    return 0;
}