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)

/*
First, solve the problem.Then write the code. - John Johnson
@author: returnAC
*/
#include <bits/stdc++.h>
using namespace std;
#define endl '\n'
#define need_for_speed ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0); // Thanks Joshua :)
#define watch(x) cout<<"->"<<#x<<" : "<<x<<endl;
#define min3(a,b,c) min(a,min(b,c))
#define max3(a,b,c) max(a,max(b,c)) 
typedef long long ll;
typedef unsigned long long llu;
const double PI = 2*acos(0.0);

signed main()
{
	//freopen("","r",stdin);
	//freopen("","w",stdout);
	need_for_speed;
	string s;
	cin>>s;
	sort(s.begin(),s.end());
	if(s[0]==s[1]&&s[2]==s[3])
		cout<<"Yes"<<endl;
	else
		cout<<"No"<<endl;
}