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: Wrong Answer)

#include <bits/stdc++.h>
using namespace std;

int main() {
    string s;
    cin >> s;
    int c1 = int(s[0]);
    int all = int(s[0]) + int(s[1]) + int(s[2]) + int(s[3]);
    int c2 = -1;
    for (int i = 1; i < 4; i++)
        if (s[0] != s[i]) {
            c2 = s[i];
            break;
        }
    if (c2 == -1)
        cout << "Yes";
    else if (all == 2 * (c1 + c2))
        cout << "Yes";
    else
        cout << "No";
    return 0;
}