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 s[4];
  for(int i=0;i<4;i++){
    scanf("%s",&s[i]);
  }

  if(s[0]==s[1]){
    if(s[2]==s[3]&&(s[0]!=s[2])){
      puts("Yes");
      return 0;
    }
  }
  if(s[0]==s[2]){
    if((s[1]==s[3])&&(s[0]!=s[1])){
      puts("Yes");
      return 0;
    }
  }
  if(s[0]==s[3]){
    if(s[1]==s[2]&&(s[0]!=s[1])){
      puts("Yes");
      return 0;
    }
  }
  puts("No");
  return 0;
}