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(void){
  char data[4];//文字
  char* result="";//文字列
  int flag=0;
  scanf("%s" , data);
  for(int i=0;i<4;i++){
    for(int j=0;j<4;j++){
      if(!(i==j) && (data[i]==data[j])){
        flag+=1;
      }
    }
  }
  if(flag==4){
      result="Yes";
  }else{
      result="No";
  }
  printf("%s",result);
  return 0;
}