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<n;++i)
using ll = long long;
using P = pair<int,int>;

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