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: Accepted)

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn main() {
    let s: String = read();
    let cv: Vec<char> = s.chars().collect();

    if cv[0] != cv[1] {
        if (cv[0] == cv[2] && cv[1] == cv[3]) || (cv[0] == cv[3] && cv[1] == cv[2]) {
            println!("Yes");
        } else {
            println!("No");
        }
    } else {
        if cv[1] != cv[2] && cv[2] == cv[3] {
            println!("Yes");
        } else {
            println!("No");
        }
    }
}