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
    integer(4):: i,ai,alphabet_counts(26) = 0, count
    character(4):: s

    read*, s

    do i=1,4
        ai=ichar(s(i:i))-64
        alphabet_counts(ai)=alphabet_counts(ai)+1
    end do

    do i=1,26
        count = alphabet_counts(i)
        if (count /= 2 .and. count/= 0) then
            print*, 'No'
            stop
        end if
    end do

    print*, 'Yes'
end program fifty_fifty