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 a[5];
  scanf("%s", a);

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