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 <stdlib.h>

int compare (const void * a, const void * b) {
   return ( *(char*)a - *(char*)b );
}

int main() {
    char word[5];
    char l[2];
    int result = 1;
    int count1, count2 = 0;

    for (int i = 0; i < 4; i++) {
        word[i] = getchar();
    }
    qsort(word, 4, sizeof(char), compare);
    if ((word[0] == word[1]) && (word[2] == word[3]) && (word[0] != word[2]))
        printf("Yes\n");
    else
        printf("No\n");
    
}