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[5];
scanf("%s", &S);

if((S[0]==S[1]&&S[2]==S[3] &&S[0]!=S[2])||
      (S[0]==S[2]&&S[1]==S[3] && S[0]!=S[1])|| 
         (S[0]==S[3]&&S[1]==S[2] &&S[0]!=S[1])){
    printf("Yes\n");
}else {
    printf("No\n");
}
return 0;
}