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(void)
{
  int c[26] = {};
  char s[4 + 1];
  scanf("%4s", s);
  for (int i = 0; i < 4; i++) {
    c[s[i] - 'A']++;
  }
  char *ans = "Yes";
  for (int i = 0; i < 26; i++) {
    if (c[i] != 0 && c[i] != 2) {
      ans = "No";
    }
  }
  puts(ans);
}