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: Wrong Answer)

#include<stdio.h>

int main() {
    char str[5];
    int a[26] = {0};
    int count = 0;

    scanf("%s", str);

    a[str[0] - 'A']++;
    a[str[1] - 'A']++;
    a[str[2] - 'A']++;
    a[str[3] - 'A']++;

    for (int i = 0; i < 26; i++) {
        if (a[i] == 2) {
            count++;
        }
    }

    if (count == 2) {
        printf("Yes¥n");
    } else {
        printf("No¥n");
    }
    
    

    return 0;
}