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 <vector>
#include <string>
#include <list>
#include <utility>
#include <algorithm>

using namespace std;

typedef long long ll;
typedef vector<ll> vl;
typedef list<ll> listl;
typedef string str;

#define min(A, B) min(static_cast<ll>(A), static_cast<ll>(B))
#define max(A, B) max(static_cast<ll>(A), static_cast<ll>(B))
#define all(x) (x).begin(), (x).end()
#define mp make_pair

#define _rep(i, m)		for(ll i = 0, i_max = m; i < i_max; i++)
#define _erep(i, m)		for(ll i = 0, i_max = m; i <= i_max; i++)
#define _brep(i, b, m)	for(ll i = b, i_max = m; i < i_max; i++)
#define _ebrep(i, b, m)	for(ll i = b, i_max = m; i <= i_max; i++)
#define _rrep(i, m)		for(ll i = m; i >= 0; i--)
#define _rerep(i, b, e)	for(ll i = b; i >= e; i--)

#define rep(m)			_rep(i, m)
#define erep(m)			_erep(i, m)
#define brep(b, m)		_brep(i, b, m)
#define ebrep(b, m)		_ebrep(i, b, m)
#define rrep(m)			_rrep(i, m)
#define rerep(b, e)		_rerep(i, b, e)

ll gcd(ll a, ll b) { return b ? gcd(b, a % b) : a; }
ll lcm(ll a, ll b) { return a * b / gcd(a, b); }

void in(ll& I)
{
	cin >> I;
}

void in(vl& I)
{
	for (auto& i : I)
	{
		cin >> i;
	}
}

void in(listl& I)
{
	for (auto& i : I)
	{
		cin >> i;
	}
}

void in(str& s)
{
	cin >> s;
}

void out(ll O)
{
	cout << O;
}

void out(vl& O)
{
	for (auto& o : O)
	{
		cout << o;
	}
}

void rout(bool b, str True, str False)
{
	if (b) cout << True.c_str();
	else cout << False.c_str();
}

int main()
{
	str s;
	
	cin >> s;
	sort(all(s));

	rout(s[0] == s[1] && s[2] == s[3] && s[1] != s[2], "Yes", "No");
	
	return 0;
}