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 s[4];
  char flag[1];
  int ans = 0;
  scanf("%c%c%c%c",&s[0],&s[1],&s[2],&s[3]);
  if(s[0] == s[1] || s[0] == s[2] || s[0] == s[3]){
    ans += 1;
  }
  if(s[1] == s[2] || s[1] == s[3])if(s[1] != s[0])ans+=1;
  if(s[2] == s[3])if(s[2] != s[0] && s[2]!= s[1])ans+=1;
  if(ans == 2) printf("Yes\n");
  else printf("No\n");
  return 0;
}