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 first, second, third, forth;
    scanf("%s" "%s" "%s" "%s", &first, &second, &third, &forth); 
    if(first == second && first != third && third == forth){
        printf("Yes\n");
    }
    else if(first == third && first != second && second == forth){
        printf("Yes\n");
    }
    else if(first == forth && first != second && third == second){
        printf("Yes\n");
    }
    else{
        printf("No\n");
    }
}