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 <bits/stdc++.h>
#define rep(i,n) for (int i = 0; i < (n); i++)
using namespace std;
using ll = long long;

int main(){
  string s;
  cin >> s;
  bool can = false;
  if(s[0]==s[1] && s[2]==s[3]) can = true;
  if(s[0]==s[3] && s[2]==s[1]) can = true;
  if(s[0]==s[1] && s[1]==s[2] && s[2]==s[3]) can = false;
  if(can) cout << "Yes" << endl;
  else cout << "No" << endl;
  return 0;
}