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(){
  char a[5];
  scanf("%s", a);
  if((a[0] == a[1] && a[1] == a[2]) || (a[0] == a[1] && a[1] == a[3]) || (a[0] == a[2] && a[2] == a[3]) || (a[1] == a[2] && a[2] == a[3])){
    printf("No");
    return 0;
  }
  if(a[0] == a[1]){
    if(a[2] == a[3]){
      printf("Yes");
      return 0;
    }
  }
  if(a[0] == a[3]){
    if(a[1] == a[2]){
      printf("Yes");
      return 0;
    }
  }
  if(a[0] == a[2]){
    if(a[1] == a[3]){
      printf("Yes");
      return 0;
    }
  }
  printf("No");
  return 0;
 }