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 <bits/stdc++.h>
using namespace std;
#define IOS ios::sync_with_stdio(false); cin.tie(0);
#define FOR(i,s,n) for(int i = s; i < (n); i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(n) (n).begin(), (n).end()
#define RALL(n) (n).rbegin(), (n).rend()
using ll = long long;
using ull = unsigned long long;

int main(void)
{
    IOS
    string s;
    cin >> s;

    if (s[0] == s[1] && s[1] == s[2]) {
        cout << "No" << endl;
        return 0;
    }
    if (s[0] == s[1]) {
        if (s[2] == s[3]) {
            cout << "Yes" << endl;
            return 0;
        }
    }
    if (s[0] == s[2]) {
        if (s[1] == s[3]) {
            cout << "Yes" << endl;
            return 0;
        }
    }
    if (s[0] == s[3]) {
        if (s[1] == s[2]) {
            cout << "Yes" << endl;
            return 0;
        }
    }
    cout << "No" << endl;

    return 0;
}