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 Lua (5.3.2) (judge verdict: Accepted)

local s = io.read("l")
local t = {}
for i=1,4 do
    local x = string.sub(s, i, i)
    t[x] = (t[x] or 0) + 1
end
for k,v in pairs(t) do
    if v ~= 2 then
        print("No")
        return
    end
end
print("Yes")