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>
#include<string.h>

int main(void)
{
  int i, cnt = 0;
  char word[5];
  int s[26];
  scanf("%s", word);
  for (i = 0; i < 26; i++)
    s[i] = 0;
  for (i = 0; i < strlen(word); i++) {
    s[word[i]-'A']++;
  }
  for (i = 0; i <= 25; i++) {
    if (s[i] == 2)
      cnt++;
  }
  if (cnt == 2)
    puts("Yes");
  else
    puts("No");
}