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 (GCC 5.4.1) (judge verdict: Accepted)

#include<stdio.h>
int main(){
  int a[26] = {0}, ans = 0;
  char s[5];
  scanf("%s", s);
  for(int i = 0; i < 4; ++i){
    a[s[i] - 65]++;
  }
  for(int i = 0; i < 26; ++i){
    
    if(a[i]) ans++;
  }
  if(ans == 2) puts("Yes");
  else puts("No");
  return 0;
}