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.split
a = s[0]
b = s[1]
c = s[2]
d = s[3]

count_a = 0
count_a += 1 if a == b
count_a += 1 if a == c
count_a += 1 if a == d

count_b = 0
count_b += 1 if b == a
count_b += 1 if b == c
count_b += 1 if b == d

count_c = 0
count_c += 1 if c == a
count_c += 1 if c == b
count_c += 1 if c == d

count_d = 0
count_d += 1 if d == a
count_d += 1 if d == b
count_d += 1 if d == c

ok = count_a == 1 && count_b == 1 && count_c == 1 && count_d == 1

puts ok ? 'Yes' : 'No'