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: Wrong Answer)

#include <stdio.h>

int main(void){
 
  /* 文字列の入力 */
  //printf("文字列を入力してください。\n");
  char S[4];
  int ret;
  ret = scanf("%s", S);
  if (S[0]==S[1]){
    if (S[2]==S[3]){
      printf("Yes");
    }else{
      printf("No");
    }
  }else{
      if((S[0]==S[2])&&(S[1]==S[3])||(S[0]==S[3])&&(S[1]==S[2])){
	      printf("Yes");
      }else{
          printf("No");
      }
  }
  return 0;
}