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)

s=gets.chomp.split("")
c1=s[0]
s.delete_at(0)
flag=true
idx=s.index(c1)
if(idx!=nil)
	s.delete_at(idx)
else
	flag=false
end
c2=s[0]
if(c1==c2)
	flag=false
end
s.shift(1)
idx=s.index(c2)
if(idx==nil)
	flag=false
end
print (flag) ? "Yes" : "No"