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(){
  char c=0,s[10],b[300]={};
  int i;
  scanf("%s",s);//printf("a\n");
  for(i=0;s[i];i++)b[s[i]]++;
  for(i=0;i<300;i++){//printf("b\n");
    if(b[i]==2)c++;
  }//printf("c\n");
  printf("%s\n",c==2?"Yes":"No");
  return 0;
}