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 Rust (1.15.1) (judge verdict: Wrong Answer)

fn get_input() -> String {
    let mut word = String::new();
    std::io::stdin().read_line(&mut word).ok();
    return word.trim().to_string();
}

fn main() {
	let mut s:Vec<char> = get_input().chars().collect();
	s.sort();
	s.dedup();
	println!("{}", if s.len() == 2 {"YES"} else {"NO"});
}