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;
    char str[4];
    scanf("%s", str);

    if(str[0] ==str[1]&& str[2]== str[3] &&str[1] !=str[2]){
        printf("Yes");
    }else if(str[0]==str[2]&&str[1] ==str[3] && str[0]!=str[1] ){
        printf("Yes");
    }else if(str[0]==str[3]&&str[1]==str[2]&& str[0]!=str[1] ){
        printf("Yes");
    }else{
        printf("No");
    }

    return 0;
}