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 Ruby (2.3.3) (judge verdict: Accepted)

input = gets.chomp.split("")
if input[0] == input[1] then
    if input[2] == input[3] then
        if input[0] == input[2] then
            print "No"
        else
            print "Yes"
        end
    else
        print "No"
    end
elsif input[0] == input[2] then
    if input[1] == input[3] then
        print "Yes"
    else
        print "No"
    end
elsif input[0] == input[3] then
    if input[1] == input[2] then
        print "Yes"
    else
        print "No"
    end
else
print "No"
end