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>
using namespace std;

int main(){
  int log=-1;
  string s;
  cin>>s;
  for(int i=1;i<4;i++){
    if(s.at(0)==s.at(i)){
      log=i;
      break;
    }
  }
  if(log==-1){
    cout<<"No"<<endl;
    return 0;
  }else if(log==2){
	if(s.at(1)==s.at(3)){
      cout<<"Yes"<<endl;
      return 0;
    }
  }else if(log==1){
    if(s.at(2)==s.at(3)){
      cout<<"Yes"<<endl;
      return 0;
    }
  }else{
    if(s.at(1)==s.at(2)){
      cout<<"Yes"<<endl;
      return 0;
    }
  }
  cout<<"No"<<endl;
}