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 <stdlib.h>
int main(){
  int i,c=0,a,v=0,b;
  char s[4];
   scanf("%s",&s);
  
  if((s[0]==s[1]&&s[2]==s[3]&&s[0]!=s[2])
     ||(s[0]==s[2]&&s[1]==s[3]&&s[0]!=s[1])
     ||(s[0]==s[3]&&s[1]==s[2]&&s[0]!=s[1]))
    printf("Yes");
  /*else if(s[0]==s[1]==s[2]==s[3])
    printf("No");*/
  else
    printf("No");
}