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 (Clang 3.8.0) (judge verdict: Wrong Answer)

#include<stdio.h>
#include<string.h>

int main(){
  int count=0;;
  char s[101];
  scanf("%s",s);
  if(s[0]==s[1]&&s[2]==s[3]&&s[0]!=s[2]){count++;}
  if(s[0]==s[2]&&s[1]==s[3]&&s[0]!=s[1]){count++;}
  if(s[0]==s[3]&&s[1]==s[2]&&s[0]!=s[1]){count++;}
  //printf("%c%c%c%c\n",s[0],s[1],s[2],s[3]);
  if(count==0){printf("%s\n","NO");}
  else{printf("%s\n","YES");}
  return 0;
}