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 i, a[4];
char s[4];
 
int main(void)
{
    scanf("%s", s);
    for (i = 0; i < 4; i++)
    {
        a[i] = s[i];
        //printf("%d\n",a[i]);
    }
    if(a[0]*4 == a[0]+a[1]+a[2]+a[3])
        {
            printf("No");
        }
        else if(a[0] != a[1]&&a[1] != a[2]&&a[2] != a[3]&&a[0] !=a[2]&&a[0] != a[3]&&a[1] != a[3]){
            printf("No");
        }else if (a[0] - a[1] == 0 && a[2] - a[3] == 0)
        {
            printf("Yes");
        }
        else if ((a[0] + a[1]) - (a[2] + a[3]) == 0)
        {
            printf("Yes");
        }
        else
        {
            printf("No");
        }
        return 0;    
}