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];
  int i,j,dem[4];
  scanf("%s", &s);
  for (i=0; i<4; i++)
    {
      dem[i]=1;
      for (j=0; j<4; j++)
        {
          if (i!=j)
            {
              if (s[i]==s[j]) dem[i]++;
            }
        }
    }
  if (dem[0]==2 && dem[1]==2 && dem[2]==2 && dem[3]==2) printf("Yes");
   else printf("No");
  return 0;
}