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 <bits/stdc++.h>
using namespace std;
#define rep(i, n)     for(int i = 0; i < (int)(n); i++)
#define rep2(i, m, n) for(int i = m; i < (int)(n); i++)
#define MOD 1000000007
#define Graph vector<vector<int>>

int main() {
  string S;
  cin >> S;

  bool ans = false;

  if(S.at(0) == S.at(1)){
    if((S.at(2) == S.at(3)) && (S.at(0) != S.at(2))) ans = true;
  }else if(S.at(0) == S.at(2)){
    if((S.at(1) == S.at(3)) && (S.at(0) != S.at(1))) ans = true;
  }else if(S.at(0) == S.at(3)) {
    if((S.at(1) == S.at(2)) && (S.at(0) != S.at(1))) ans = true;
  }

  if(ans){
    cout << "Yes" << endl;
  }else{
    cout << "No" << endl;
  }
  return 0;
}