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)
{
    char s[4];
    int i;
    int j;
    int judge[4];

    for(i = 0; i < 4; i++){
        judge[i] = 0;
    }

    scanf("%s", s);

    for(i = 0; i < 4; i++){
        for(j = 0; j < 4; j++){
            if(s[i] == s[j]){
                judge[i]++;
            }
        }
    }

    for(i = 0; i < 4; i++){
        if(judge[i] != 2){
            printf("No\n");
            return 0;
        }
    }

    printf("Yes\n");
    return 0;
}