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>
#include<stdlib.h>
#define df 0


int main(){
  int i,a,b,flag=1;
  char S[5],p,q;
  scanf("%s",S);
  p=S[0];
  for(i=1;i<4;i++){
    if(S[i]==p){
      a=i;
      b=a%3+1;
      break;
    }
  }
  if(i==4)flag=0;
  else if(S[a]==S[b] || S[b]!=S[6-a-b])flag=0;

  printf("%s",flag?"Yes":"No");
  return 0;
}


/// confirm df==1 ///