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;
 
int main() {
  char c[4];
  for (int i = 0; i < 4; i++ ){
    cin >> c[i] ;
  }
  if (c[0] == c[1]){
    if (c[2] == c[3] && c[0] != c[2]) printf("Yes\n");
    else printf("No\n");
  }
  else if (c[0] == c[2]){
    if (c[1] == c[3] && c[0] != c[1]) printf("Yes\n");
    else printf("No\n");
  }
  else if (c[0] == c[3]){
    if (c[1] == c[2] && c[0] != c[2]) printf("Yes\n");
    else printf("No\n");
  }
  else printf("No\n");
}