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 */
#include <bits/stdc++.h>
#include <boost/algorithm/string/trim.hpp>
#include <boost/range/algorithm.hpp>

/* using */
using namespace std;

/* main constructor */
struct Fast
{
    Fast()
    {
        std::cin.tie(0);
        ios::sync_with_stdio(0);
        //cout << fixed << setprecision(12);
    }
} fast;

/* template */
template <class T>
bool chmax(T &a, const T &b) { return (a < b) ? (a = b, 1) : 0; }
template <class T>
bool chmin(T &a, const T &b) { return (b < a) ? (a = b, 1) : 0; }

/* define */
#define REP(i, x, n) for (int i = x; i < (int)(n); ++i)
#define RREP(i, x, n) for (int i = x - 1; i >= (int)(n); --i)
#define rep(i, n) REP(i, 0, n)
#define reps(i, n) REP(i, 1, n + 1)
#define rrep(i, n) RREP(i, n, 0)
#define each(i, n) for (auto &i : n)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define eunique(x)  \
    boost::sort(x); \
    (x).erase(unique(all(x)), (x).end())
#define mp make_pair

/* const */
const int inf = 1e9 + 7;
const int dxl[8] = {1, 0, -1, 0, 1, -1, -1, 1};
const int dyl[8] = {0, 1, 0, -1, 1, 1, -1, -1};
const int dxs[4] = {1, 0, -1, 0};
const int dys[4] = {0, 1, 0, -1};

/* main */
signed main(void)
{
    string s;
    cin >> s;
    boost::sort(s);
    if (s[0] == s[1] && s[2] == s[3])
    {
        cout << "Yes" << endl;
    }
    else
    {
        cout << "No" << endl;
    }
    return 0;
}