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)

use std::io;

fn main() {
    let mut input = String::new();

    io::stdin().read_line(&mut input).unwrap();

    let input = input.trim();
    let mut s = vec!();

    for c in input.chars() {
        s.push(c);
    }

    s.sort();

    let res = if s[0] == s[1] && s[1] != s[2] && s[2] == s[3] {
        "Yes"
    } else {
        "No"
    };

    println!("{}", res);
}