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(){

  int count = 0, countnot = 0;
  char a[5];
  scanf("%s", a);
  for(int i= 0; i < 3; i++){
    for(int j = i + 1; j < 4; j++){
      if(a[i] == a[j]){
	count++;
      }	else{
	countnot++;
      }
    }
  }
  //printf("%d",count);
  //printf("%d",countnot);
  if(count == 2 && countnot == 4){
    printf("Yes\n");
  }	else{
    printf("No\n");
  }
  return 0;
}