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<string>
#include<cmath>
#include<algorithm>/*toupperとかが入っている*/
#include<vector>/*可変長配列vectorのインクルード*/

const int MOD=1000000007;/* 1,000,000,007 で割った余りを出力する　のとき使う*/
using namespace std;/*標準名前空間を利用する。cinやcoutはこれによって利用可能になる*/

string S;
int count;

int main(void) {
  cin >> S;

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