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: Runtime Error)

#include <iostream>
#include <iomanip>
#include <vector>
#include <algorithm>
#include <numeric>
#include <functional>
#include <cmath>
#include <string>
#include <map>
#include <queue>
#include <stack>
#define FOR(arg, ini, end) for(int arg = ini; arg < end; arg++)


using namespace std;
int main(int argc, const char * argv[]) {
    
    int n; cin >> n;
    if (n%2!=0) {
        cout << 0 << endl;
        return 0;
    }

    vector<int> d(n);
    FOR(i, 0, n) {
        cin >> d[i];
    }

    sort(d.begin(), d.end());
    int mid = n/2;
    cout << d[mid] - d[mid-1] << endl;

    return 0;
}