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 Fortran (gfortran v4.8.4) (judge verdict: Accepted)

program fifty_fifty
  implicit none
  character(4) :: s
  integer :: a(26), i
  a = 0
  read(*,*) s
  do i = 1, 4
    a(ichar(s(i:i))-64) = a(ichar(s(i:i))-64)+1
  end do
  if (maxval(a).eq.2.and.minval(a,a.gt.0).eq.2) then
    write(*,'(a)') "Yes"
  else
    write(*,'(a)') "No"
  end if
  stop
end program fifty_fifty